Witnesses to a huge warehouse fire in Whetstone described seeing fireballs billowing into the air as firefighters battled 40ft flames.

A row of derelict warehouses in Allum Way caught fire at 9.30pm last night and investigators are still working to establish the cause of the blaze.

Mother-of-three Debbie James lives 100 yards from the old buildings and was putting her children to bed when she heard a loud crackling noise.

She said: “I raised the blind and just saw a huge amount of black smoke billowing out. It was really raging – we could see the flames above the trees from our house.

“It took hold so quickly. You could feel the heat of it from outside my house. It was the biggest fire I’ve ever seen first-hand.”

Charlie Bateson, 18, said he heard what sounded like fireworks coming from behind his house in Blakeney Close.

He said: “I looked out and could see the flames through the trees. The fire was so big it looked like it was in our road. I was a bit worried but the fire brigade turned up pretty quickly.

“There were quite a few fireballs that went up and you could hear windows shattering.”

London Fire Brigade received 61 calls about the incident and crews had the blaze under control by 10.30pm.

Investigators were this morning trying to establish the cause of the incident and Barnet Council workers are still attempting to trace the owner and make the buildings safe.

Crowds of people gathered in the surrounding streets as emergency services dealt with the inferno, and some people travelled from the other side of the borough to establish the source of the smoke, which could be seen from miles away.

Mrs James said the warehouses, formerly used as a plastic bag factory, have been derelict since about 1987.

She added that the site has become an attraction for local teenagers who hang about and daub graffiti on the disused buildings.

Police were also called to the site by another neighbour last week.

Mrs James said: “It’s just slowly gone to rack and ruin over recent years. I’m always kicking kids out because it is so dangerous. Sometimes I’ve threatened to call the police.

“We had gypsies in there about two weeks ago who were there for six to seven weeks. They left behind a caravan which I think attracted more kids and they took the scaffolding, which made the buildings more unstable. It has been a problem over the years.”