Dozens of firefighters are fighting a blaze in a power tools business at an industrial estate.
Norfolk Fire and Rescue Service urged people to avoid the area around Rackheath Industrial Estate while they deal with the fire at Power Tool Services in Earl Road.
No one has been hurt.
Businesses on other parts of the estate remain open, although Norfolk police have evacuated people from nearby buildings including the snooker club.
Fire control said there were still appliances at the scene but that crews were beginning to be stood down after more than five hours tackling the blaze, adding that the fire 'was starting to die down.'
A huge plume of smoke could be seen for a large area around the scene.
Serious damage has been done to the industrial unit and the contents inside.
Peter Rowe, group manager and incident commander, said: 'At 9 o'clock this morning we received a call from the owner to report a fire in his industrial unit.
'We arrived at the scene and saw a well-established fire. Because of the contents of the building we are staying defensive.
'Our plan is to protect the adjoining buildings. I imagine we will be tackling the fire for most of the day.
'Very serious damage has been done. A lot will be gone or damaged.
'We are doing our best to stop it spreading to adjoining buildings.'
The shocked owner did not want to speak in detail about what had happened but said he was inside and got out to call the emergency services.
Six crews as well as specialist appliances are tackling the blaze and a drone is being used to check for hotspots.
Police are also on the scene assisting the fire brigade.
Special inspector Mike Chambers said: 'We have evacuated the snooker club and put a cordon in place.
'We are monitoring people and stopping them from entering the area.'
Norfolk Fire and Rescue Service tweeted at just after 10.30am: 'Please be advised we are currently dealing with a fire in an industrial unit in Rackheath.
'We strongly advise to avoid the area. As a precautionary measure we recommend closing doors and windows if you live in the vicinity.'
One worker said he had seen five fire engines on his way into work. He said he could see smoke billowing up, but no flames.
A local business owner who rents a number of local units said he had received a call about the fire and arrived to see the smoke.
Hayley Lee works in an office nearby and said: 'The first I knew about it was when I heard the sirens at 9.15am. I then saw a little smoke which got worse as the time went on.'
In January 2011. Rackheath Industrial Estate was the scene of an explosion which completely destroyed a cafe on the site.
The explosion happened at night, but it caused chaos on the estate for the next few days.
The following year, a major fire ripped through the PHS Datashred paper recycling factory on the estate. It caused serious structural damage to the building, with 60 firefighters tackling the blaze at its height.
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