Firefighters were this morning set to return to the scene of a blaze which destroyed a long-standing Norwich business, as the factory manager described his family's heartbreak at the fire.

Emotional staff watched helplessly yesterday as fierce flames and thick smoke consumed Broadland Hams on the Sweetbriar industrial estate in the north of the city right at the start of their Christmas rush.

Firefighters were still at the scene late into last night, having prevented any risk of the fire spreading to other buildings.

But general manager Edward Porter, whose father John built the Burnett Road factory in 1986, vowed that they would not be beaten.

He said: 'Nothing will be salvageable but we hope to quickly find other premises and machinery so we can supply our customers again in the very near future.'

He said it was a difficult time for his father who had established the company after first running two local butchers' shops.

Mr Porter added: 'Some of our 25 staff have been with us a long time. One woman joined when she was 16 and is now in her 40s.'

Workers returning from their lunch break raised the alarm at about 1.30pm yesterday after smelling smoke.

The first firefighters arrived at 1.50pm but the danger posed by the rapidly spreading blaze quickly thwarted attempts to fight it from inside using breathing apparatus.

Richard Herrell, group manager for Norfolk Fire and Rescue Services, said: 'The fire is very difficult to extinguish because the roof is constructed of sandwich panels of polystyrene, a highly combustible material associated with firefighters' deaths in the past.

'The first firefighters made highly commendable efforts to fight the blaze aggressively from inside but we had to pull them out because of the danger from the roof which had no sprinklers.'

He said their efforts were focused on stopping the fire spreading to the site's refrigeration plant, which contained explosive gases, and to neighbouring buildings. The fire was too difficult to put out and there would have to be a controlled burn-out.

Fire crews were due to return to the site today to check for any remaining hot-spots.

All the staff had been evacuated safely from the building. with only one person slightly affected by smoke inhalation.

Workplaces downwind were evacuated as plumes of thick black smoke became visible across the city, obscuring visibility on the nearby ring road at one stage.

Firefighters came from as far afield as Earlham, Sprowston, Carrow, Hethersett, Wroxham, Long Stratton, Wymondham, Aylsham, Attleborough and Great Yarmouth.

Eight fire engines were called, including an aerial ladder platform which was put into action to douse the burning roof from above.

One of the first eye-witnesses on the scene was former firefighter Jay Steward, from Acle, who had been in a nearby Burger King with his family.

He said: 'We followed the first fire engine here. The fire struck at the back of the building and spread. Firefighters started off inside but were later withdrawn, They have certainly lost the building.'

Arlene White, from the neighbouring Pentagon Control Systems building, said: 'We smelled the fire and then saw the fire engines arriving.

'We were quickly evacuated because of the danger of toxic smoke.'

Louise Hall, who works in an office block in Burnett Road, watched it through a window and described it 'getting worse and worse'.

'The whole side of the building seems to be on fire, and it's bellowing out flames,' she said.

By 6pm last night fire crews had contained the fire, ruling out the possibility of it spreading further than the ham factory.

Around six appliances remained at 8pm, as the burn-out continued, with relief crews being drafted in. Crews from Sprowston, Watton, Hethersett and Earlham were the last to leave the scene in the early hours of the morning, but fire crews will return today to keep an eye on the site.

The factory, which had started gearing up for Christmas, produces ham, bacon, gammon and sausages for shops and catering outlets across East Anglia.