Bird flu has been confirmed at a farm near Attleborough - the fourth Norfolk case this month in a worsening regional outbreak.
Government vets found a highly-pathogenic strain of avian influenza at a commercial poultry farm, close to another case which was confirmed on September 19.
Defra said all birds on the infected premises will be humanely culled, and a 3km Protection Zone and 10km Surveillance Zone have been set up around the site.
The latest case was confirmed on the same day that a raft of new restrictions were enforced for all poultry keepers across Norfolk, Suffolk and parts of Essex in a bid to halt a rising number of cases in the area.
The regional Avian Influenza Prevention Zone (AIPZ) makes it a legal requirement for all bird keepers in the affected area - from commercial farms to backyard hobbyists - to follow heightened biosecurity rules to protect their flocks.
Deputy chief veterinary officer Richard Irvine said: "All bird keepers in the region must urgently take action now to both prevent disease getting in to flocks and it spreading any further."
The disease is a major concern for the region's poultry industry, as well as for its wild bird colonies, where reported cases have also been rising.
John Newton, Norfolk county adviser for the National Farmers' Union (NFU), said the new cases are "concerning news for our region’s vital poultry sector", and he urged all bird keepers to "maintain enhanced biosecurity measures to help prevent future outbreaks".
Meanwhile, disease control activities including a mass cull of poultry have been completed following an earlier outbreak confirmed at a farm near Gayton in west Norfolk on August 21.
A Defra statement says the 3km Protection Zone around the premises has now been lifted "following successful completion of disease control activities and surveillance within the disease control zones surrounding this premises". However the 10km Surveillance Zone remains in place.
Although avian influenza can be devastating for wild birds and poultry flocks, the UK Health Security Agency advise that the risk to public health is very low and the Food Standards Agency says avian influenzas pose a very low food safety risk.
For full details on the requirements and boundaries of the AIPZ, see www.gov.uk/guidance/avian-influenza-bird-flu
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