15/11/2015 1:22 PM AEDT | Updated 15/07/2016 12:51 PM AEST

Australian Father And Son In Bataclan Theatre Horror

An Australian father has told of the horrific moment he lost his 12 year-old son amid the terror and bloodshed of the Bataclan theatre massacre in Paris on Friday night.

John Leader, 46, an Australian who has lived in Paris for 15 years, told London's Telegraph newspaper that he and his son Oscar hid inside the theatre as gunmen systematically killed hostages.

His first act as shooting began was to hide his son.

"I pushed Oscar to the other side of the mixing desk. People were three or four deep hiding there. The lights suddenly went on. It had been dark but now there were full house lights. Everybody went quiet. It was clinical. All you heard was bang, bang, bang. The shooter was standing at the back of the hall and targeting people at the front. He was taking aim. He was not spraying. It was clinical. He was aiming: aim, fire, aim, fire, aim, fire," Mr Leader said.

"Everyone was thinking: if I move I’m dead."

Mr Leader, who is the director of an environmental company, said the mixing engineer waved his son to go back because the attackers had a full view of the other side of the desk.

"He tried to get up but I told him: “Stay down, these guys are killers.”

Mr Leader said that he heard one of the attackers say something about Syria, and that he felt that there was no chance that anyone would overpower them and the hope was that they would run out of ammunition. After a pause in shooting, someone yelled "they are gone" he said.

"To my right I saw people running and saw that someone had opened an exit door. I grabbed Oscar and said “Let’s go!” Then we saw a lake of blood and bodies lying everywhere.

"But we had to hit the deck again because there was more shooting. During another lull I pushed Oscar towards the stairs that led to the exit. I ended up being about five seconds behind him getting out, and when I did get outside he was gone.

"I saw a crowd of people about 50 metres away, running. I thought he was with them. I screamed “Oscar” and was expecting to see him turn around. But no.

"I went back to the exit and up the stairs. By now there were bodies on the stairs, I think maybe of people who had been shot and had dragged themselves towards the exit. I couldn’t see Oscar. And then the shooting started again and I went outside.

"I walked down the road and turned right and asked a cop there if he had seen my son. He said no and that I should get out of the area immediately. Then I called Oscar on his mobile and he told me he was okay and was nearby. I ran to meet him. He’d lost his wallet and his shoes during our escape from the Bataclan," Mr Leader said.

It is believed that 89 people were killed during the attack by four gunmen at the Bataclan Theatre, which was filled with fans of the American band Eagles of Death Metal. Three of the gunmen reportedly activated their suicide vests, while a fourth gunmen was shot dead by police as they stormed the theatre.

A total of 129 people were killed during the co-ordinated attacks on the French capital on Friday night, with another 352 wounded, 99 of them are in a critical condition.