Survivors from the catastrophic rock concert late Friday have described fleeing over bodies to hide after gunmen began executing rock fans in a barrage of automatic gunfire.

"It was horrible inside, a bloodbath, people shot in the head, people who were shot as they were lying on the ground," said a police officer who took part in the operation to storm the venue where 1,500 people had been attending a rock concert.

At least 82 people were killed in the concert hall by four black-clad attackers who opened fire with automatic weapons on the packed venue, sowing carnage and panic. "At first we thought it was part of the show but we quickly understood," said radio presenter Pierre Janaszak who was sitting in the balcony with his sister and friends when they heard shots from below about an hour into the concert.

"They didn't stop firing. There was blood everywhere, corpses everywhere. We heard screaming. Everyone was trying to flee." They hid in a toilet where they would spend the next two hours waiting for police to storm the building.

"They had 20 hostages, and we could hear them talking with them," Janaszak said.

"I clearly heard them say 'It's the fault of Hollande, it's the fault of your president, he should not have intervened in Syria'," he said.

The attack was claimed on Saturday morning by the Islamic State group.

By Saturday morning, the historic venue known for hosting rock concerts was still cordoned off, its gaudy red-and-yellow facade giving little sign of the carnage inside, an AFP correspondent said.

One of the policemen involved in storming the venue returned early on Saturday, saying what had happened had not yet sunk in for him.

"I went back home to reassure my children. Now I've just come back as a person" to try and comprehend the horror, he told AFP, "to do sort of a personal debriefing. You simply cannot remain indifferent."

Outside a bright yellow sign reading 'Eagles' glowed intact and just in front stood the tour bus belonging to the Eagles of Death Metal, the US rock band that had been playing when the attackers struck. "I don't understand!" said a local resident called Peggy, her eyes red. "This is a place where young people come to party."

Friday saw a total of six separate attacks, which killed at least 128 people in Paris, one targeting the national stadium where the French and German national football teams were playing a friendly.

"This is just disgusting, it's apocalyptic," said a man called Mamadou who was in a bar near the Bataclan watching the match on TV when the attacks took place.

"I have no words, it's just ridiculous," he told AFP, saying he was convinced Islamic State militants were behind the attack -- for which IS later indeed claimed responsibility.

"People yelled, screamed and everybody was lying on the floor, and it lasted for 10 minutes, 10 minutes, 10 horrific minutes where everybody was on the floor covering their heads," Julien Pearce, a reporter for France's Europe 1 radio station told CNN. "We heard so many gunshots and the terrorists were very calm, very determined and they reloaded three or four times."

"It was a bloodbath." He said he saw the face of one gunman who was probably 20 to 25 years old. "There's nothing but the sound of gunfire and carnage running through my head," said another young woman who hid in a side room with around 25 others.

"We had one chance in two of taking a bullet," she said, shaking.

By around 6:30 am (0530 GMT), a string of vehicles could be seen evacuating the bodies of the victims, an AFP correspondent said. Outside the concert hall, a swarm of police vans blocked the view of the building as hundreds of cameras of the world's press gathered at the site.

"Are there any more of them still out there?" a young man asked a policeman at the scene. "We don't know. It's possible but you mustn't give in to panic," the officer replied.

"That's what they want."

Nearby, another local, tears in his eyes, asked if he could put a candle it in front of the restaurant La Belle Equipe. "It's too early. Much too early," said a policewoman, gently sending him away.