POLICE are calling on local residents to help piece together what caused 20ft flames to rip through Blackburn business units on Saturday night.

Hundreds of people saw Rockfield Mill, in Rockfields Street, go up in smoke at 8.30pm as 40 firefighters battled to save three companies.

Firm owner, Kevin Shanley, watched in horror as it took just two hours for his business of 19 years to be reduced to ashes.

And one couple had to be evacuated from their flat in a cordoned-off area between Hall Street, New Garden Street, Highfield Road and Bankside for safety.

Police are investigating whether the fire was started by a teenage prank.

Station officer Aidan Fortune led the operation to tackle the blaze, which narrowly avoided an acetylene and propane explosion. Two aerial platforms poured 500,000 litres of canal water onto the flames, while jets penned in the fire on four sides. Eight engines attended.

"There were a hundred cylinders of acetylene and propane, and if that had gone we would have faced a major 24-hour evacuation," said Mr Fortune. "The fire was well alight when we arrived and access was difficult. It was quickly stopped from spreading but it was lucky it was so close to the canal."

Mr Shanley, owner of Shanley's garage recovery business since 1985, fought back tears as he watched his warehouse go up in flames. "This is the first time I have had to face anything like this," he said.

"The building is 140 years old. We have all the tools inside but I have no idea what we will do it is not safe inside. I feel totally sick."

Four people employed by Mr Shanley were today waiting for news about the future.

North West Tippers and Rhino's are also based in the warehouse. Owner of the former, Chris Nuttall, said he had 60 new wagons in his building and had to switch all the alarms off.

"The firefighter led me through my section and there was at least two feet of water on the floor with sparks flying everywhere. There is a lot of money in there."

Black smoke could be seen as far away as Belmont and hundreds of people watched the emergency crews in action.

Sergeant Dave Sherrington, of Blackburn Police, said: "Propane gas cylinders were a major concern and we feared there would be a big explosion.

"The investigation continued on Sunday to establish the cause."

Detective Inspector Simon Giles added: "We have been interviewing a juvenile girl who is not being charged. We need residents to explain what has been going on before the fire broke out."

Anyone with information should call police on 01254 353569.