The highly pathogenic H5N1 strain of avian influenza was confirmed in a large commercial poultry premises between Thetford and Swaffham on November 30.
Defra says all poultry on the infected premises will be humanely culled, while a 3km protection zone and 10km surveillance zone have also been declared around the site.
A similar outbreak was declared at another site near Mundford on November 25.
The virus has taken a toll on East Anglia’s poultry farms during the run-up to the busy Christmas season, with 10 confirmed cases in Norfolk, and a further six in Suffolk since the end of October. Several have been in the Breckland area, where there is a high concentration of poultry farms.
To stop the outbreak growing, a mandatory order has been enforced nationally, which means all keepers with more than 50 captive birds of any species – or any number of poultry kept to give away or sell eggs or poultry products – must house them indoors.