Paris: An emotional Charlie Hebdo columnist described the horrific scene that greeted him after his colleagues were shot dead at the French satirical newspaper's office and said "I couldn't save them".

Patrick Pelloux would normally have been at the editorial meeting that was the main scene of the attack that left 12 dead.

However on Wednesday, in his other job as head of the emergency room doctors' association in France, he was attending a meeting elsewhere in Paris to improve links between the different emergency services.

"I was at this meeting when Jean Luc, the graphic artist (of Charlie Hebdo) called me to tell me: You have to come here quickly, they have shot at us with a Kalashnikov," Pelloux told AFP in a phone interview.

"I thought it was a joke, but it wasn't. When I arrived it was dreadful," he said, choking with emotion.

Pelloux arrived at the offices three minutes after the attack with a high-ranking fire department official, who Pelloux said acted "heroically" as he triggered the emergency response.

"And as we were taking care of the victims, they (the attackers), were still on the streets killing people," Pelloux said.

Five of France's best-known cartoonists were killed in the attack.

Charlie Hebdo's 47-year-old editor-in-chief, Stephane "Charb" Charbonnier, who was also one of its cartoonists, was murdered along with the police bodyguard assigned to him following death threats.

Pelloux described the bloody scene in the editorial meeting room.

In a separate interview on the iTele channel, Pelloux said he had called French President Francois Hollande just after the attack.

"He said 'I'm on my way'. The president wanted to speak to us when he saw that the newspaper was in difficulty this summer," Pelloux said.

"We had gone to see him. The president wanted to change the laws so that these newspapers could continue to exist."

The Charlie Hebdo columnist said despite the killing of the paper's top staff, he was "optimistic" after seeing the solidarity expressed in the wake of the attacks by both heads of state and ordinary people who had taken to the streets.