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.
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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.