A state of emergency has been declared in France after a night of terror in Paris that is feared to have left around 140 people dead.
There were two suicide attacks and a bombing near the Stade de France stadium, shootings at restaurants and a massacre inside a popular music venue in what is the worst violence to hit France since the Second World War.
Eight attackers died, including seven in suicide bombings, but the city's prosecutor said it is possible there are still terrorists on the run.
Security has been stepped up and border control checks re-imposed after the attacks, which President Francois Hollande described as an "abomination".
In horrific scenes officers stormed the Bataclan concert hall where hostages were being held but attackers, wearing suicide belts, blew themselves up, leaving more than 100 people dead.
During a visit to the concert hall in the early hours Mr Hollande, who has cancelled his trip to the G-20 meeting in Turkey, said the country will be "merciless" against those who have attacked them.
"We will lead the fight. We will be merciless," he said.
Various numbers of victims have been reported killed, but a Paris city hall spokesman on Friday night said the death toll was at least 140 people.
The national football side was playing a friendly match against Germany at the Stade de France when two suicide attacks and a bombing took place nearby.
President Hollande had been at the stadium but was evacuated. Tens of thousands of people fell silent at the stadium on Friday night in tribute to those killed and injured.
Gregory Goupil of the Alliance Police Nationale said there were at least three dead in the attacks near the stadium. He said the explosions went off simultaneously.
As many as 18 people died when the terrace of the Rue de Charonne was sprayed with gunfire, while around 14 people were killed when Le Carillon bar-cafe, and the nearby Cambodian restaurant Le Petit Cambodge, were also shot at, prosecutor Francois Molins said.
Two hundred people were injured in the string of attacks, French media reported.
Scenes of "carnage" were described by witnesses at the Bataclan, who said there was "blood everywhere".
World leaders including Barack Obama and David Cameron have spoken of their shock and outrage at the violence.
The Prince of Wales is to send Mr Hollande a message of "profound sympathy and solidarity with the people of Paris", a Clarence House spokeswoman said
The Foreign Office said it was in "close touch" with the French authorities and it was "urgently investigating" whether there were any British victims.
The attacks come after the Charlie Hebdo atrocity, which took place in January and saw 12 people killed after gunmen stormed the offices of the satirical magazine.
They also come a day after Islamic State militant Mohammed Emwazi, known as Jihadi John, was targeted in a US air strike in Syria. It is not clear if there is any link.
US president Mr 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."
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 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."
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 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."
The Bataclan concert hall had been due to host a concert by US rock band Eagles Of Death Metal. All of the group have been accounted for and are safe, a US official said.
The Foreign Office advised Britons to "exercise caution in public places" following the attacks and people with concerns about British friends or relatives in Paris can 0207 0081500 for assistance.