PRECAUTIONARY testing of every staff member at Bernard Matthews’ Great Witchingham site after several workers tested positive for the virus.
The firm said food production and safety were unaffected, adding that staff with positive tests were self-isolating.
A small cluster of cases has also hit Bernard Matthews’ Holton food processing site.
There are 1,000 workers at the Great Witchingham processing plant, and authorities said there was no evidence to suggest transmission of the virus at the site.
Louise Smith, Norfolk’s director of public health, said: “Our top priority is to reduce the spread of the coronavirus, which will help to protect the staff at Bernard Matthews and the public.
“This testing is a sensible, precautionary measure that will help us understand who at the site has COVID-19 and who else they may have been in contact with.
“While there is currently no evidence to suggest widespread transmission at the Great Witchingham site, we know that testing can help to understand and contain the spread of the virus.”
A spokesman for Bernard Matthews added: “We can confirm a small number of positive cases at our site at Great Witchingham.
“These colleagues and their contacts are now self-isolating at home, and we will continue to work closely with public health officials to monitor the situation.
“There is no evidence these transmissions occurred in the factory. Food production and safety remain unaffected.”