The cull of 159,000 turkeys on the Suffolk farm where bird flu broke out is finished, the government has said.
The operation to gas the birds at the Bernard Matthews plant was completed after nearly 48 hours, the environment department Defra confirmed.
Earlier, Environment Secretary David Miliband said he was determined to "stamp out" the bird flu outbreak.
Strict controls are in place around the site near Lowestoft, but officials say the risk to humans is "negligible".
However, the government says it is preparing for the "very remote possibility" the disease could mutate into a form that could spread from human to human, causing a flu pandemic.
The Department of Health has taken the advice of scientists to stockpile enough Tamiflu anti-virals to cover a quarter of the population.
A large-scale preparatory exercise was carried out last week.
Experts are trying to find the source of the outbreak of the disease, identified as the "highly pathogenic" Asian strain of the H5N1 bird flu virus.
A 3km (1.9 miles) protection zone and a 10km (6.2 miles) surveillance zone are in place around the farm, in Holton.
The carcasses of the birds are being transported to a rendering plant in Cheddleton, Staffordshire, for incineration.
BBC correspondent Richard Bilton said the cleaning and disinfection of the area could last for weeks.
Mr Miliband told MPs the response to the outbreak of the H5N1 strain had been "rapid, well co-ordinated and appropriate".
Speaking in the Commons, he said the Food Standards Agency had assured him there was no risk to people eating properly cooked poultry, including turkey and eggs.
"Our goals in this case are clear. To stamp out the disease, protect public health, to protect animal health and welfare, and to regain disease-free status for the UK."
He said it was also a "very high priority" to discover the cause of the outbreak, and that while the most likely cause was a link with wild birds, all possibilities were being considered.
But the Royal Society for the Protection of Birds said speculation about the virus being passed on by wild birds was "premature".
Shadow environment secretary Peter Ainsworth said the government needed to stress to the public that eating poultry was "entirely safe".
Poultry owners in a wider restricted zone, covering 2,090 sq km (807 sq miles) around Holton, have been told to keep their flocks isolated from wild birds.
But BBC reporters discovered some chickens left outside just a mile from the farm.
Rural Affairs minister Ben Bradshaw told the BBC that officials would be scouring the area to make sure biosecurity was being adhered to.
The H5N1 virus, which causes bird flu, does not pose a large-scale threat to humans, as it cannot pass easily from one person to another.
Experts, however, fear the virus could mutate at some point in the future, and in its new form trigger a flu pandemic, potentially putting millions of human lives at risk.
Scene of outbreak
All poultry to be culled
Visitors disinfected and restricted access
3km Protection Zone
Poultry kept indoors and tested
10km Surveillance Zone
No movement of poultry to or from area except for slaughter
Trains carrying live poultry are prevented from stopping in the protection zone
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.
Isolation of poultry from wild birds
Poultry movements to be licensed