Around 200 north Norfolk factory staff are still waiting for the go-ahead to return to work, three days after a serious blaze closed their plant.

An investigation is under way into the cause of the fire, in an industrial fat fryer at Heinz Frozen and Chilled Foods, which broke out at teatime on Friday.

The factory, on Station Road, Westwick, near North Walsham, has been closed since the incident which saw more than 90 firefighters striving to contain the blaze at its height on Friday night.

The fire was eventually extinguished on Saturday and a spokesman for Heinz said the company had finished contacting all its employees that day, telling them they would not be needed to work their current block of shifts, for which they would still be paid. Staff usually work a 12-hour shift pattern round-the-clock.

The spokesman said yesterday that the investigation, which is being carried out jointly by the fire service and Heinz, was likely to take several days. He added that the fire had been confined to one specific production area.

Production of the Aunt Bessie's frozen potato products range would not resume until a full assessment had been made. The spokesman added that the fire brigade had confirmed there was no further risk at the site. He added: 'Of course safety remains our first priority.'

The shift of 50 to 60 staff working on the site when the fire broke out were unharmed. Neighbours in homes around the factory had also been kept informed, said the spokesman.