A massive police operation is taking place in London today after seven people were killed, and 48 more were wounded, in last night's terror attack on London Bridge and in the Borough Market area of the city.
The three attackers drive a white van along London Bridge, ploughing into people, before carrying out stab attacks in the busy Borough Market area.
The NHS has confirmed that 21 of those injured in the attack are in critical condition.
On Sunday witnesses described hearing shots as police arrested several people in connection with the ttack.
Residents said armed officers swooped on flats in Barking, east London, where they believe one of the attackers may have lived.
At least four police vans were stationed behind a cordon outside the Elizabeth Fry flats in King's Road.
Veronica Oladapo, 45, who lives in a neighbouring block, left her building at around 7am to see police taking four men and a woman away.
She said: "When I came out they were already taking some of the casualties away.
Whatever the United States can do to help out in London and the U. K., we will be there - WE ARE WITH YOU. GOD BLESS!— Donald J. Trump (@realDonaldTrump) June 3, 2017
"There were three of them ... the ambulance came and took them away.
"There were another two sitting down inside."
One of the men had a hood pulled over his head while another one used a jacket to hide his face, she said.
Damien Pettit, 31, said he thought one of the attackers was possibly a neighbour who lived on the ground floor of his apartment block.
He told the Press Association: "He's lived here for about three years. He's one of our neighbours. I've said hello in passing more than 50/60 occasions. He has two young kids, he was a very nice guy."
He said it would be "a bit of a shock" if his neighbour was confirmed as one of the attackers.
Mr Pettit said he had seen a photo which appeared to show "one of the attackers upside down on the floor wearing camouflage trousers, which he (the neighbour) was wearing two days ago".
He said he immediately thought of his neighbour but could not confirm if it was definitely the same man as the attacker in the picture was face down.
More than five hours after the first arrests, a woman in a burka was led into a police van parked outside the flats.
It then drove away with sirens blazing, followed by three other vans.
Scotland Yard said 12 people had been detained in Barking "in connection with last night's incidents" and that searches at a number of addresses in the area were continuing.
A neighbour in Barking said one of the attackers, a man believed to be of Pakistani origin, had recently asked him where he could hire a van.
Ken Chigbo told Sky News that the man quizzed him about the van he was using to move house and where he could get one for himself.
Mr Chigbo, who spoke with the attacker on Saturday, said: "We were having a general conversation because I am in the process of moving house at the moment.
"I had a big van up here and he came up to me and said, 'Oh, Ken, you are moving'. He was usually a really nice, friendly guy but this time it was on a different level of nice.
"It was quite strange and hard to put into words.
"He was asking me where I am moving to, and then he started asking about the van.
"He said to me, 'Oh, where did you get your van, Ken? How much is it, is it possible to get in automatic?' - all these specific questions about the van, which obviously now makes sense in my head.
"At the time I didn't think anything of it."
Images of the van used by the attackers appear to show it is a white Hertz hire van, which also has B&Q branding on it.
A spokesman for Hertz said: "Our thoughts are with those affected by the terrible incident in London last night.
"We are assisting the authorities and are unable to comment further at this stage due to the ongoing police investigation."
A spokesman for B&Q referred all inquiries to the police.
Attackers brought carnage to the streets of the capital, stabbing a police officer and revellers with 12-inch knives, reportedly shouting "this is for Allah".
Police were called at around 10.08pm on Saturday night to reports of a vehicle striking pedestrians on London Bridge.
The white van then continued to drive to Borough Market.
Three men then left the vehicle and began to stab people, including a British Transport Police Officer;
The suspects were confronted and shot by police at Borough Market within eight minutes of the first emergency call being made.
The trio were pictured wearing what appeared to be explosive vests, with police later confirming they were fake. Mrs May said they were "worn only to spread panic and fear".
"We took 48 patients to five hospitals across London and treated a number of others at the scene for minor injuries," Peter Rhodes, London Ambulance Service's assistant director of operations, said in a statement on Sunday.
NHS England says that 21 people injured in the London Bridge terror attack are in a critical condition.
Speaking shortly before 4am police told reporters they believed no more than three suspects were involved in the terrifying incident but said enquiries are ongoing to be "100pc confident" on that.
Police chiefs also pledged that Londoners will see an increased police presence in the city in the coming days and said the policing plan for the city will be reviewed.
The incident was described by police as a "protracted" attack which began on London Bridge and ended in the nearby food market.
The Department of Foreign Affairs issued a statement to Independent.ie, saying there are no reports of any Irish citizens having been involved,
"We continue to closely monitor the situation in London following last night's attack," it read.
"There are no reports of Irish citizens having been involved.
"Anyone who has serious concerns about loved ones can contact the Department of Foreign Affairs and Trade in Dublin on 01 408 2000, or the Irish Embassy in London on 0044 207 235 2171."
Armed police rushed to the scene where shots were heard and authorities urged Londoners on Twitter to "run, hide, tell" if they were caught in the attack.
The attacks come days ahead of a June 8 election and less than two weeks after a suicide bomber killed 22 people at a pop concert by U.S. singer Ariana Grande in Manchester in northern England. There was no immediate claim of responsibility.
The BBC showed a photograph of two possible London attackers shot by police, one of whom had canisters strapped to his body. Hours after the attack the area remained sealed off. However, police have confirmed that the 'devices' were fake.
Images soon emerged on social media of the horror attack. One photographer Gabriele Sciotto shared two images of what appears to be one of the attackers being apprehended by police. The attacker's reportedly false suicide vest if visible in the images.
Police said that their knowledge of the incident was "still growing".
"Armed response officers then responded very quickly and bravely and confronted the three male suspects who were shot and killed on Borough Market," Mark Rowley, Britain's top anti-terrorism officer, said.
"Sadly, six people have died in addition to the three attackers shot by police," he said.
"The suspects had been confronted and shot by police within eight minutes of the first call. The suspects were wearing what looked like explosive vests but these were later established to be hoaxes," he said.
An on-duty British Transport Police officer received "serious injuries" including head, face and leg wounds, as he responded to calls for help from the public.
Speaking at a press conference this morning, London's Met Police Commissioner Cressida Dick confirmed the death toll has risen to seven.
"I visited hospital this morning and heard about brave actions of my officers," she said.
"I also heard about brave members of emergency services and members of the public who rushed towards danger to help.
"I pay tribute to all who came to aid of those in need during this dreadful attack.
"Our priority now is to establish more details about these individuals who carried out the attack.
"I would ask Londoners and visitors to remain calm and vigilant. Don't hesitate to contact us if you see anything suspicious," she continued.
"We were on a high level of alertness. We were prepared potentially for an incident as we have been for some time.
"Our understanding is that three people were involved in the attack - we believe the threat they posed was neutralised within eight minutes.
"We don't believe there is anyone else outstanding. We will seek to establish if anyone else was assisting the attackers.
"We will do everything in our power to stop a horrendous act such as this."
The Commissioner also responded to questions from the media, and said she believes they will be sharing appropriate information with the US.
Streets around London Bridge and Borough Market, fashionable districts packed with bars and restaurants, would have been busy with people on a Saturday night out. BBC showed dozens of people, evidently caught up in the attack, being escorted through a police cordon with their hands on their heads.
Witnesses described a white van careering into pedestrians near London Bridge and knocking over several people.
"It looked like he was aiming for groups of people. I froze because I didn't know what to do," Mark Roberts, 53, a management consultant, told Reuters. He saw at least six people on the ground after the van veered on and off the pavement.
"It was horrendous," he said.
A taxi driver told the BBC that three men got out of the van with long knives and "went randomly along Borough High Street stabbing people."
Witnesses said people ran into a bar to seek shelter.
"People started running and screaming, and the van crashes into the railing behind. We went towards Borough Market and everyone went inside (the bar). Everyone in the bar started pushing people from the exits," one witness who gave his name as Brian, 32, told Reuters.
Another witness, who declined to be named, his white top covered in blood, described a scene of panic in the bar.
"They hit the emergency alarm. There was a line of people going down to the emergency exit. And then people started screaming coming back up," the 31-year-old said.
"Around the corner there was a guy with a stab wound on his neck ... There was a doctor in the pub and she helped him. They put pressure on the stab wound."
BBC radio said witnesses saw people throwing tables and chairs at the perpetrators of the attack to protect themselves.
One witness told BBC News television; "I walked up to London Bridge and I just saw this geezer stabbing someone, he had blood down him. He was there with two mates and all three of them were stabbing this girl, they just attacked her. They stabbed another girl. I was in shock. I started running. I was shouting, "Terror attack!"
"I started running and shouting and everybody started running. I followed the guys. They went down towards Borough Market, they stabbed a bouncer at a club, they ran into all the pubs and all the bars. I was shouting at people to run. I tried to help as many people as I could, but I couldn't.
"I was throwing stools and chairs around so people could get out. They stabbed this girl, I don't know how many times, maybe 10 times, she was crying for help and I couldn't, I tried to."
Islamic State call
Islamic State earlier on Saturday sent out a call on instant messaging service Telegram urging its followers to launch attacks with trucks, knives and guns against "Crusaders" during the Muslim holy month of Ramadan.
Similar attacks, in Berlin, Nice, Brussels and Paris, have been carried out by militants over the past couple of years.
"Following updates from police and security officials, I can confirm that the terrible incident in London is being treated as a potential act of terrorism," Prime Minister Theresa May said.
London's Thames river police said it was working with the lifeboat rescue service to help evacuate people caught up in the attack.
U.S. President Donald Trump took to Twitter to offer U.S. help to Britain. The White House said he had been briefed on the incidents by his national security team.
One woman told Reuters she saw what appeared to be three people with knife wounds and possibly their throats cut at London Bridge at the Thames river. Reuters was unable to immediately verify her account.
The incident bore similarities to a March attack on Westminster Bridge, west of London Bridge, in which a man killed five people after driving into a crowd of pedestrians before stabbing a police officer in the grounds of parliament.
Several witnesses also reported hearing gunshots around London Bridge.
"We were in an Uber (taxi) going towards London Bridge and suddenly we saw people running. The Uber stopped, we asked people what was going on – people said there was shooting," said Yoann Belmere, 40, a French banker living in London.
"Now the area is completely closed with police cars going one way and ambulances going the other," he told Reuters.
A witness told CNN two men had entered a restaurant in the Borough Market area and stabbed two people inside. He said a waitress was stabbed in the throat and a man was stabbed in the back.
The Manchester bombing on May 22 was the deadliest attack in Britain since July 2005, when four British Muslim suicide bombers killed 52 people in coordinated attacks on London's transport network.
People staying in the Premier Inn Bankside were also evacuated across Southwark Bridge.
Dozens, including children, were brought across the bridge by police after the fire alarm in the hotel went off, according to one.
Emergency services were seen treating people lying injured at the junction of Thrale Street and Southwark Street, near Borough Market.
One woman was taken away on a stretcher while others sat injured on the ground, with shocked people crying and shouting around them.
Frightened people were led up Southwark Street away from Southwark Bridge Road, and police officers were seen screaming to people and ordering them to run.
Many were in tears, with friends supporting each other and carrying people up the road.
Cordons were put up across Southwark Street before repeatedly being pushed back as police widened the critical zone around Borough Market.
The police have opened a phone line for people worried about friends or family in London, while urging people who are safe to make contact with their family.
Here is a timeline of how the events unfolded:
10.08pm: Police are called to reports of a van hitting pedestrians on London Bridge. It is initially unclear whether the van deliberately drove into people but the similarities with the Westminster Bridge terror attack are obvious and armed police are on the scene.
10.30pm: Witness accounts emerge of the van driving into a crowd of people at "about 50mph", leaving at least six casualties on the ground. BBC journalist Holly Jones tells how she narrowly avoided being hit, jumping out of the way of the van. There are unconfirmed reports of people being stabbed and shots being fired.
10.40pm: Police say they are dealing with a major incident and warn people to stay away from the area.
11.15pm: Scotland Yard says it is dealing with a second serious incident in the nearby Borough Market. Three men carrying large knives are seen attacking passersby in the street. People in restaurants reportedly try to fight off the attackers with chairs. Armed and unarmed officers flood the area, telling some people to leave. Video footage in a restaurant in the area shows police telling diners to get down on the floor. Gunshots are heard.
11.30pm: A police officer setting up a cordon tells people to move away from the area and stop filming. Sounding emotional, she says "people have died".
11.45pm: Police say they are searching for three men suspected of carrying out the attacks.
11.50pm: A third incident is reported in Vauxhall, but police later say this is believed to be an unrelated stabbing.
11.55pm: British Transport Police confirm there have been "multiple casualties".
12.10am: Officials say Theresa May is travelling to Downing Street for briefing from security officials and will chair a meeting of the the emergency Cobra committee later on Sunday. She says the incidents are being treated as "potential" acts of terror and praises the emergency services.
12.25am: Both the incidents at London Bridge and Borough Market are declared "terrorist incidents" by police.
1.30am: Three loud bangs are heard in the Borough Market area.
1.50am: A photograph shows two men lying on the ground after being shot by police. One had canisters of some kind strapped to his body.
4am: Police say six people were killed before three suspects were shot dead by armed police. The canisters appeared to be "hoax" suicide bombs. Thirty people are being treated in hospitals around London.
6.15am: London Ambulance Service reports 48 injured people are now being treated in hospitals in the city.
Additional reporting: PA and Reuters
U.S. President Donald Trump took to Twitter amid the unfolding deadly drama in London on Saturday to offer U.S. help to Britain and to promote his controversial travel ban as an extra level of security for Americans.