A cull of thousands of birds is under way after bird flu was confirmed in turkeys on a Suffolk farm.
Officials are beginning to clear the carcasses of the dead turkeys
The virus was discovered at Redgrave Park Farm near Diss, where all 6,500 birds are being slaughtered.
Vets are carrying out further tests on the turkeys at the centre of the outbreak to try to determine if they have the virulent H5N1 strain.
A 3km protection zone and a 10km surveillance zone have been set up and the farm is co-operating with vets.
Officials said the outbreak was of the H5 strain, but it was yet not known if it was H5N1, which can be fatal to humans.
Police officers are at the entrance to the farm, and vehicles are being sprayed with a jet hose.
The Department for Environment Food and Rural Affairs (Defra) confirmed preliminary tests showed the free-range turkeys at the farm had the H5 strain of bird flu.
Some 10% of birds in one shed had died during one night, it said, adding that further tests were needed to see if the virus was H5N1, which has killed some 200 people worldwide.
At the affected premises, all birds - including approximately 5,000 turkeys, 1,000 ducks and 500 geese - will be slaughtered.
The BBC's Andrew Sinclair, who is at the scene, said large trucks and gas canisters had been moved on to the premises earlier in preparation for the cull.
It is expected that all the birds will be gassed and then put in sealed containers.
Officials said further local surveillance work would happen before deciding on any culls on neighbouring farms.
Heather Peck, Defra's regional operations manager for animal health, said: "The top priority is to get controls in place, to inform people of the controls in place and that's largely done electronically these days.
"The immediate priority for us here is both to cull the affected birds on the infected premises and to establish any possible contact or any potential traces of movement between those premises, or related premises or premises in the immediate vicinity."
Redgrave Park Farm is owned by poultry producer Gressingham Foods.
It said that all employees at the site had been given antiviral drugs as a precaution and that the birds on the site had been moved indoors.
William Buchanan, the firm's operational directors, said: "Sixty turkeys out of a flock of 1,000 from one house on the site were found dead. The site was immediately isolated and additional bio-security measures imposed."
Inside the protection and surveillance zones, bird movements are being restricted and all birds housed or isolated from contact with wild birds.
All keepers on the British poultry register are also being notified about the outbreak and EU officials have been informed.
National Farmers' Union (NFU) president Peter Kendall said it had been a "summer and autumn from hell" for livestock farmers who were "punch drunk" following earlier outbreaks of foot-and-mouth, bluetongue and flooding.
The farm's directors said they were co-operating with Defra
The disease was discovered on Sunday by a vet, who noticed that there had been an increasing number of deaths among turkeys in one of the five sheds on the farm.
Acting Chief Veterinary Officer Fred Landeg said the risk of bird flu spreading was increased during the autumn months because of wild bird migration.
The affected birds were free-range - meaning they had access to the outdoors and may have been of greater risk of catching the disease.
Ciaran Nelson of the RSPB said he was concerned that migratory birds will be blamed for the outbreak.
"No wild birds have been reported with the disease in Europe since the end of August. There are a number of other ways that it could have got here and we must not jump to conclusions at this stage."
Consumer confidence is a big concern for the poultry industry, and the Food Standards Agency reassured customers that there was no threat to human health so long as eggs and poultry were properly cooked.
The NFU insisted that turkey supply over Christmas would not be affected, as the cull accounted for only a small proportion of the 10 million festive turkeys sold each year.
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