Some 3,900 chickens were found dead on a farm in southwest Miyazaki prefecture over the weekend, prompting local authorities to slaughter the remaining 8,100 birds as part of efforts to contain the deadly virus.

"The examination conducted at the National Institute of Animal Health confirmed that the bird flu virus detected in Miyazaki prefecture was the H5N1 strain," the agriculture ministry said in a statement.

It urged the public to stay calm, saying there were no known cases of humans contracting the virus after eating poultry.

Local agricultural officials began incinerating all 12,000 dead birds Monday on the farm, some 900 kilometers southwest of Tokyo, in an effort to stop the outbreak spreading.

They put the farm under a massive sanitation program while ordering 11 other poultry farms within a 10-kilometer radius not to move chickens and eggs.

"We have taken thorough measures based on the worst case scenario," said Koji Ishikawa, a health official in Miyazaki prefecture.

"Regardless of whether it is H5N1 or H5N2, we still don't know exactly how damaging the viruses would be to human health," he told AFP.