CUSTOMS road fuel investigators are assisting detectives in probing a mystery explosion which devastated a Bolton garage and workshop -- only yards away from terraced homes.

Three lorry tankers loaded with diesel fuel exploded in the inferno. Firefighters prevented the blaze from spreading to a further two tankers.

As revealed in yesterday afternoon blast at the Trescon premises on Weston Street, Great Lever destroyed one "nissen-hut" type building within the grounds.

The blast -- the second similar incident on the same site over the last 10 years -- could be heard more than a mile away and was fought be a team of up to 35 firefighters aided by four special incident units.

Fire investigators have established that large quantities of diesel fuel were involved in the blaze but they have yet to establish how the explosion was caused.

They were also faced with acetylene bottles inside the premises which had to be taken out to prevent them from also exploding.

Assistant Divisional Officer Ray Grimes of Bolton Central Fire Station said that five lorry tankers full of what they believe was diesel fuel were involved in the fire. Three were well alight when firefighters arrived.

Police and firefighters -- who were at the scene of the explosion for more than four hours -- were joined last night by investigators from HM Customs and Excise Road Fuel Investigation department who have launched their own inquiry into the incident.

Residents and passers-by people in Weston Street were alerted yesterday afternoon by a series of five loud bangs coming from the site.

Motorist John Robinson had just parked his car outside the premises when the explosion happened.

"I heard two loud bangs and then the smoke and flames came from the site," he said. "The police and fire brigade were here almost straight away but it looked like the fire services were having trouble getting into the premises."

Weston Street resident Rubina Ahmad heard the explosions and ran out of her home in panic.

She said: "I was in the kitchen making my baby's dinner when I heard the bangs and came out to the front. I could see the smoke and flames, it was quite worrying."

Mrs Ahmad quickly went to the aid of a 70-year-old resident who lived across the street next door to the garage workshop premises.

Mrs Ahmad revealed that yesterday's incident was the second explosion at the site within 10 years. Last time residents had to be evacuated to Burnden Park.

Another resident, who did not wish to be named, added: "We thought the place was closed. We didn't see anyone coming or going and the gates were closed. We didn't know what was inside. Our children play football close by because we thought it was safe."

ADO Grimes confirmed that the front gates to the property were locked when they arrived but said they discovered that a back gate to the premises had been left open.

"We did not know what was inside the building so we treated it as a full chemical incident and we had officers wearing special chemical incident suits inside the building," he said.

Site owner Patrick Cassidy, who was called to the scene, told police that the garage units were leased out and he did not know what was inside. Shortly after his arrival firefighters were able to establish that no chemicals were involved.

Mr Cassidy declined to comment: "I have absolutely nothing to say whatsoever," he said.

Chief Insp Alan Green, head of Bolton police uniform operations said: "It is too early to say whether the cause of the explosion was deliberate but this cannot be ruled out."