Terrorism struck at the heart of London last night after a vehicle veered off the road and mowed down pedestrians on London Bridge and gunshots rang out amid reports of knife attacks at nearby Borough Market.
The violence turned a summery Saturday night in an area full of bars and restaurants into a scene of panic and chaos, with officers running through crowded streets screaming for people to flee and lifeboats drafted to help clear the area.
At least two people were killed in the rampage and it was reported that up to seven were feared dead.
British Prime Minister Theresa May said it was a terrorist attack and the Metropolitan Police force confirmed that it had declared the attacks "terrorist incidents".
Police said they were called just after 10pm to reports of a vehicle hitting pedestrians on the bridge, which crosses the River Thames in central London.
Soon after, there were reported stabbings at nearby Borough Market, an area full of bars and restaurants.
Metropolitan Police said armed officers were sent to the scenes and shots were fired. They did not say if officers fired the shots. The force initially said officers were also responding to a reported third incident, in the Vauxhall area of London. But they said later that turned out to be an unrelated stabbing.
Police tweeted a warning telling people in the area to run to safety, hide and then call police if safe to do so.
May said that "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".
She said it was a fast-moving investigation and her thoughts were with "those who are caught up in these dreadful events."
May's office said she would chair a meeting of the government's COBRA emergency committee on Sunday.
About two hours after the first reports of an incident, television images showed people walking away from the London Bridge area with their hands on their heads. Police tweeted that Londoners should "remain calm but be alert and vigilant".
Nick Brandon of British Transport Police said the force had received reports of "multiple" casualties in an incident possibly involving a knife and a vehicle. He said he did not know how serious the injuries were.
Multiple witnesses reported a vehicle veering off the road and hitting several pedestrians; others also said they saw a man with a knife.
Witnesses reported seeing injured people on the ground on the bridge. One witness, Holly Jones, told the BBC a white van veered off the road and struck as many as six people. She said she saw at least four or five people on the ground.
Another witness, Will Heaven, said he saw people who appeared to have been hit, and one being put into an ambulance.
"We saw injured people on the road, injured people on the pavement," he told Sky News.
He added that "it did not look like an accident", saying it was clear that police "thought they were responding to something far more serious than a road traffic accident."
A man who gave only his first name, Ben, told BBC radio that he "saw a man in red with a large blade, at a guess 10 inches long, stabbing a man, about three times" near Borough Market.
Tony Murphy, a former serviceman, heard the incident unfold from his nearby flat on Upper Thames Street.
"There was tremendous gunfire. At first I thought it was fireworks, then I recognised it was significant gunfire. Only afterwards - 10 minutes after - did the emergency services come."
Transport for London said busy London Bridge station and two others were closed at the request of police.
The incident happened on a warm Saturday night in a busy area full of bars and restaurants. It comes less than three months after an attacker ran down people with a vehicle on Westminster Bridge, killing four, then stabbed a policeman to death outside parliament.
On May 22, a suicide bomber killed 22 people and injured dozens at an Ariana Grande concert in Manchester. After that attack, Britain's official threat level from terrorism was raised to "critical," meaning an attack may be imminent. Several days later it was lowered to "severe," meaning an attack is highly likely.
In a statement Taoiseach Enda Kenny said: "Terrible news coming from London - we stand with our close neighbours again tonight."