India has detected its first cases of the deadly H5N1 bird flu strain in western Maharashtra state.
A huge cull is to begin
Dr HK Pradhan of High Security Animal Disease Laboratory said tests had confirmed the virus in dead chickens.
The health ministry said that though no human cases had been detected so far, some people were being tested for the disease.
The H5N1 strain has killed at least 90 people since early 2003, mostly in south-east Asia.
The virus can infect humans in close contact with birds. There is still no evidence that it can be passed from human to human.
Maharashtra minister Anees Ahmed said about 50,000 birds had died at a chicken farm at Nandurbar district near Maharashtra's border with Gujarat state in the past few days.
He said that tests of the samples of the dead birds had confirmed bird flu.
Mr Ahmed said more than half a million chickens in the affected area would be culled in the next 24 hours to prevent the disease from spreading to human beings.
Another million chicken in farms located 10km around the affected area would be vaccinated.
Mr Ahmed said the state government was sending a team of 200 veterinary doctors to the area, more than 400km (250 miles) northeast of Mumbai.
"We have not decided on whether to evacuate people from the area," he was quoted as saying by the Associated Press.
A 3-km (2-mile) safety cordon has been established around the site where the dead birds were found.
The European Union recently approved a series of measures to try to halt the spread of the virus, including the automatic creation of protection and surveillance zones around outbreaks in wild birds.
If the virus transfers from wild birds to poultry, "buffer zones" that could cover an entire region should be established and the transport of poultry restricted within them.
The BBC's Zubair Ahmed in the western Indian city of Mumbai (Bombay), capital of Maharashtra, says for the past few weeks there were suspicions in Nandurbar of the outbreak of the disease after deaths of thousands of chickens.
A poultry owner in the area said 400,000 chickens in poultry farms had been affected by the virus.
Indian health officials have advised people against eating chicken until further notice.
The World Health Organization says at least 91 people in seven countries have died of the H5N1 strain of bird flu since 2003.
Almost all the deaths have been linked to contact with infected poultry.
Experts fear the virus could combine or mutate into a form that passes easily between humans, possibly sparking a pandemic, but there is no evidence that this has happened yet.