As many as 159,000 birds are to be culled after it emerged that avian flu killed 2,600 turkeys at a Suffolk farm.
The bodies of the dead birds are being piled up in containers
According to the European Commission the birds at the Bernard Matthews farm, Holton, tested positive for the H5N1 strain, which can kill humans.
Vets were called to the farm late on Thursday night, said the Department of Environment, Food and Rural Affairs.
A three-kilometre protection zone and a 10km surveillance zone has now been set up around the farm.
A Defra spokeswoman said the risk of the disease spreading to humans was low and there was no need for panic.
She added: "Avian influenza is a disease of birds and whilst it can pass very rarely and with difficulty to humans, this requires extremely close contact with infected birds, particularly faeces."
Defra said there were 159,000 other turkeys on the farm.
The farm has been placed under tight restrictions and samples from the dead birds were examined at the Veterinary Laboratories Agency in Weybridge, Surrey.
Bart Dalla Mura, Bernard Matthews commercial director, said the birds had not been imported and were raised in a shed.
He told BBC News: "We're going to work with Defra to find out how this has occurred. The critical thing is that it has been contained."
"There is no risk to consumers at all," he added.
Defra said the alarm was raised by the farmer after he noticed "significant mortality" among his flock.
The first deaths happened on Tuesday 30 January when 71 chicks died, said Defra.
A further 186 died the following day and 860 died on 1 February.
Some 1,500 died on Thursday, making a total of 2,617.
There are 15 types of bird, or avian, flu. The most contagious strains, which are usually fatal in birds, are H5 and H7.
There are nine different types of H5. The nine all take different forms - some are highly pathogenic, while some are fairly harmless.
The type currently causing concern is the deadly strain H5N1, which can prove fatal to humans.
In May last year, more than 50,000 chickens were culled after an outbreak of the H7 bird flu in farms in the neighbouring county of Norfolk.
One member of staff at the farm contracted the disease and was treated for an eye infection.
In March 2006, a wild swan found dead in Cellardyke, Fife, was found to have the H5N1 strain of the virus, which has been responsible for the deaths of more than 100 people, mostly in Asia.
Suffolk County Council have set up a bird flu helpline on 08456 032 814.
WHEN BIRD FLU HITS THE UK
1: Scene of outbreak
All poultry to be culled
Visitors disinfected and restricted access
2: 3km Protection Zone
Poultry kept indoors and tested
3: 10km Surveillance Zone
No movement of poultry to or from area except for slaughter
Rail transport restricted to non-stopping movements
Bird fairs and markets banned
Increased surveillance of wetland areas
Domestic birds not to share water used by wild birds
Footpath restrictions likely only on free-range farms
People in towns not affected unless they keep poultry.