Food safety officers have moved onto a duck farm in Redgrave, near Diss, where up to 55,000 of the animals are to be culled.
The precautionary action today follows the discovery of the bird flu virus at the Gressingham Foods site.
It is the second time the disease has been identified in the area within a month, after Defra and Animal and Plant Health Agency (APHA) identified the H5N8 strain of avian influenza (AI) virus at a nearby broiler breeding unit run by Banham Group.
About 23,000 chickens were culled after that discovery.
A spokesman from Gressingham Foods said the cull was a voluntary precaution, and stressed that no birds had tested positive for the bird flu.
He said the strain of the disease had been found in the environment, rather than in its ducks, following routine tests.
The spokesman said: 'There is not and has not been any outbreak of AI in any of our flocks, which are tested by Defra regularly.
'This is a precautionary measure as Defra consider the farm to have potential for dangerous contact with the infected neighbouring farm.'
The spokesman said Gressignham had been on high alert for bio-security risks since this current strain of AI was first found in Europe in autumn last year. He said: 'Non-essential visits have been cancelled and management movements between farms and species have been restricted.
'The welfare of our birds and food safety to our customers are absolute priorities and we work to independently audited, stringent standards in hygiene, bio-security and animal welfare.'
Details of how the cull was being carried out were not released, but a Defra spokesman said it was 'humane'.
After the cull, the premises will be cleansed and disinfected to reduce the risk to other birds.
A Defra spokesman said: 'A 3km protection zone and a 10km surveillance zone, already in place around the neighbouring site, will be continued.
'Our investigations will continue and the restrictions already placed on the site will remain in force until cleansing and disinfection is finished and the investigation is complete. Public Health England advises that the risk to public health from the virus is very low and the Food Standards Agency is clear that bird flu does not pose a food safety risk for UK customers.'
An interactive map of bird flu incidents in the UK can be found at www.gisdiseasemap.defra.gov.uk/intmaps/avian/map.jsp
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