France declares state of emergency after dozens killed in Paris
France has declared a state of emergency and closed its borders after dozens of people were killed in violence in Paris.
Around 100 people have reportedly been taken hostage at a theatre after the French capital was hit by a series of attacks.
French president Francois Hollande said he was closing the country's borders and declaring a state of emergency.
Officials have said between 35 to 40 people have been killed, the Associated Press reported.
Officials said shots were fired in at least two restaurants and at least two explosions were heard near the Stade de France stadium, where the national side was playing Germany in a friendly football match.
President Hollande left the stadium, where he had been watching the game, to hold an emergency meeting.
Prime Minister David Cameron said: "I am shocked by events in Paris tonight. Our thoughts and prayers are with the French people. We will do whatever we can to help."
A Foreign Office spokeswoman said: "We are very concerned about the attacks in Paris. We are in close touch with the French authorities and are urgently investigating whether there are any British nationals caught up in this."
Eyewitness Ben Grant said he was in a bar with his wife when the gunshots were fired and he had seen six or seven bodies on the ground.
He told the BBC: "I was told people in cars had opened fire on the bar.
"There are lots of dead people. It's pretty horrific to be honest.
"I was at the back of the bar. I couldn't see anything.
"I heard gunshots. People dropped to the ground. We put a table over our heads to protect us.
"We were held up in the bar because there was a pile of bodies in front of us."
The attacks come almost a year after the Charlie Hebdo atrocity, which took place in January and saw 12 people killed after gunmen stormed the offices of the satirical magazine.
In June, France launched a terrorism investigation after police found a decapitated body in a gas factory in the south-eastern city of Lyon.
Two months later three Americans and one Briton were awarded medals for bravery after they overpowered a heavily armed gunman on a Paris-bound train.
Pictures on social media showed hundreds of football fans had spilled on to the pitch at the Stade de France after the game ended.
US president Barack Obama told a press conference that the violence in Paris "was an attack on all of humanity".
He said: "Those who think they can terrorise the people of France and the values they stand for are wrong."
Outside a restaurant thought to have been attacked, around 30 people were seen standing - many with their hands on their heads - on the closed road outside their cars.
Another image shows an armed member of the Paris police force crouching alongside a small dining table outside a restaurant. Glasses of wine and cutlery remain untouched on the table, while a candle still burns alongside them.
The gates at the Oberkampf metro station - which is the nearest station to the Bataclan Concert Hall - have been closed, while footage shot from a nearby flat shows a troop of around 20 policemen rushing down the road in a close unit.
Pictures on social media from Rue Oberkampf show a long line of around 40 people, including one man with a small dog, who appear to be waiting for further instruction while police oversee the situation.
At least three ambulances have reached the Rue Oberkampf, while a collection of armed policemen gathered in a group of at least 20 at a junction on the road, according to an image taken from a high window.
A French police union official said there were two suicide attacks and a bombing near the Stade de France stadium.
The official, Gregory Goupil of the Alliance Police Nationale, whose region includes the area of the stadium, said there were at least three dead in the attacks near the stadium, near two of the entrances and a McDonald's restaurant.
He said the explosions went off simultaneously.
Automatic gunfire has been heard outside the theatre where the hostages are being held.
Images on social media showed handfuls of people outside the Bataclan theatre, including two men who were ushered away with an ambulance team with blood clearly visible on their shirts.
Television cameraman Charles Pitt said he was outside a cafe in the city's 11th arrondissement where people were shot at around 9.10pm local time.
He told BBC News: "I had just walked past the front of the cafe. It's a popular, typical French cafe. People were sitting outside.
"I had literally gone about 30 metres when, I thought it was a firecracker to start with, and then it went on and it got louder.
"It went on for a minute. Everybody dived for cover thinking it was gunfire. Then there was a pause for about 15 seconds and then it all started up again.
"Then it calmed down a bit and I walked back to the front of the cafe and there was a whole pile of bodies, probably about seven on the left-hand side and four that had been sitting on the tables outside on the right-hand side, and a lot of injured.,
"I saw a woman who had obviously been shot in the leg.
"Then the police turned up. Now we're about 75 metres away. A lot of fire brigade, a lot of police, a lot of army patrolling the streets."
A France 24 reporter close to the scene said loud "cracks and bangs" which sounded like gunfire had come from the Bataclan in the last few minutes. The venue had been due to host a concert by US rock Band Eagles Of Death Metal.
Parisian taxi drivers have reportedly turned off their meters to carry people home for free.
Police officials confirmed security forces have launched an assault on the theatre where the hostages have been taken, AP reported.
The Foreign Office said people with concerns about British friends or relatives in Paris can call the main switchboard number 0207 0081500 for assistance.
A statement on Eagles Of Death Metal's Facebook page said: "We are still currently trying to determine the safety and whereabouts of all our band and crew. Our thoughts are with all of the people involved in this tragic situation."
The Foreign Office advised Britons to "exercise caution in public places" following the attacks.
Updated travel advice said: " There have been a number shooting incidents in central Paris (10th/11th arrondissements) resulting in a number of casualties.
"There have been a number of explosions near to the Stade de France stadium, also resulting in casualties. You are advised to exercise caution in public places and follow the advice of the local authorities. French Government advice is to stay indoors."
People with concerns about a family member can contact the Embassy in Paris on 00 33 144513100.
Metropolitan Police Commissioner Sir Bernard Hogan-Howe said: "My thoughts and those of Met officers and staff are with Paris and the men and women whose job is to deal with this horrific situation.
"London and Paris are linked as two of the world's strongest capital cities and we stand prepared to help in any way."