The blaze was still smoking on Monday

Panasonic has lost a month's production - 26,000 microwave ovens, 4,000 televisions and thousands of digital set top boxes had been destroyed - at the start of the crucial Christmas trading period.

Factory units in the area were evacuated when the alarm was raised, shortly after 1945GMT, in a successful attempt to stop the fire spreading to a nearby Boots warehouse containing pharmaceutical equipment.

At its height, the fire was tackled by 70 firefighters and took nearly five hours to bring under control.

No-one was injured but police are keeping an open mind it started.

South Wales Police Detective Inspector Gary Sullivan said his team were already interviewing the half dozen staff on duty at the time of the fire to see of they could help throw some light on a possible cause.

At its height, 70 firefighters were involved

He said: "We're making inquiries initially from factory-to-factory and within the community.

"We're also talking to a number of staff - the staff who were working the night in question - and then any immediate lines of inquiry."

South Wales Fire Service forensic experts have started the painstaking process of looking for the clues to how the fire broke out.

Assistant Divisional Officer Mick Flanagan said: "As the building is made safe, in conjunction with the demolition workers, we'll then begin to demolish and excavate parts of the building."

Panasonic spokesman Chris Doherty said the firm was already assessing how to cover the lost production.

"Hopefully we will be able to put appropriate recovery measures in so that we don't leave any shortages in the shops at this key time."

The firm's Cardiff production factory is nearby