About 6,500 birds are being slaughtered after avian flu was confirmed in turkeys on a Suffolk farm, government officials have announced.
Thousands of turkeys and other birds are being slaughtered
The H5 strain was found in turkeys at Redgrave Park Farm near Diss. All birds on the farm, which include ducks and geese, are to be slaughtered.
A 3km protection zone and a 10km surveillance zone have been set up.
The government could not yet confirm if the birds had the highly pathogenic H5N1 strain, a spokeswoman said.
Police officers have been seen at the entrance to the farm, and vehicles are being sprayed with a jet hose.
A statement issued by the Department for Environment Food and Rural Affairs (Defra) said that preliminary tests showed the turkeys had the H5 strain of bird flu. It is not yet known whether it is H5N1, which has killed some 200 people worldwide.
All birds are being slaughtered at the premises, and Defra said it was consulting on what further measures may be needed.
It is expected that all the birds will be gassed and then put in sealed containers, officials said.
The birds include approximately 5,000 turkeys, 1,000 ducks and 500 geese, a Defra spokeswoman added.
Inside the zones, bird movements will be restricted and all birds must be housed or isolated from contact with wild birds.
All poultry keepers on the British poultry register will be notified and EU officials have been informed.
Geoffrey Buchanan, operations director of Redgrave Poultry, which rents the farm, said that all employees at the site had been given antiviral drugs as a precaution.
He added that all the birds on the site were now indoors, and that he hoped this would be a contained outbreak.
National Farmers' Union president Peter Kendall said: "Obviously this is another huge blow to the farming industry, which is still dealing with the effects of bluetongue and foot-and-mouth."
Acting Chief Veterinary Officer Fred Landeg said that laboratory results on what type of bird flu it was were expected "in the next 24 hours".
Defra officials said that 10% of birds in one shed died over one night.
Susan Watts, science editor of the BBC's Newsnight, said that this would seem to suggest that the outbreak involved a highly pathogenic strain of the virus.
Mr Landeg told BBC Radio 5Live that 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.
Results on Monday morning showed that the flu was of the H5 type - but more tests were needed to ascertain whether it is the dangerous variant.
He said that the risk of bird flu spreading was increased during the autumn months because of wild bird migration.
Mr Landeg confirmed that the affected birds were free-range - meaning they had access to the outdoors and may have been of greater risk of catching the disease.
A statement released on behalf of poultry producer Bernard Matthews said the affected farm was not owned by the company, and none of the firm's farms fell within the exclusion zone.
Earlier this year bird flu was discovered at a Bernard Matthews turkey farm in Suffolk.
More than 160,000 birds were killed after an outbreak of the virulent H5N1 strain of the disease on the farm in February.
The Food Standards Agency reassured consumers that there was no threat to human health so long as eggs and poultry were properly cooked.
And National Farmers' Union poultry board chairman Charles Bourns insisted that turkey supply over Christmas would not be affected.
He added that the cull accounted for only a small proportion of the 10m festive turkeys sold each year.