Five fire crews were called to Spencer Street in St James yesterday lunchtime after reports of a fire inside an empty factory.

But when firefighters arrived at the scene they needed to help two people away from the site and to safety.

Station manager Gavin Ellis said: "There were two persons inside who had to be led to safety.

"However, after that there was no life risk to anyone so we decided not to send any firefighters into the building."

Police said they were treating the fire as arson but, although two people helped the police with enquiries yesterday, no arrests were made.

Fire officer Mick Rodden, of the county's arson task force, said: "It seems to have been a deliberate fire but we are keeping an open mind at the moment."

The industrial unit, on the edge of St James Mill industrial estate, is surrounded by houses, and police cordoned off the street and advised residents to stay indoors.

Witnesses who saw the fire crews arrive described a large plume of smoke coming from the building.

One man said: "I work at the Westbridge depot and I came along because I could smell the smoke from about a mile away."

A 34-year-old woman said: "I just walked down here to see a friend in Spencer Street but I can't get beyond the cordon.

"It looked pretty serious to me because of the amount of firemen there."

The flames had died down within half-an-hour but firefighters still needed to let fumes out.

People caught outside the cordon watched as firefighters mounted on an aerial appliance used a disc cutter to slice open the sheet metal roof and ventilate the main factory unit.

They also used an infrared camera to detect hotspots within the building.

Crews were being particularly cautious because the heat may have caused heavy sandwich panels inside the unit to become unstuck and fall.
Firefighters also said they feared that fire could lie undetected behind the panels.

Mr Ellis said: "We were adopting a very defensive approach.

"With no one at risk we were taking things slowly."

The police cordon was removed at about 2pm although, because of the panels, the inside of the building still posed a danger to firefighters yesterday afternoon.

Mr Rodden said he would try to trace the owners of the factory to help with his enquiry into the cause of the blaze.