An outbreak of bird flu at a poultry farm in southwestern Japan was caused by the H5N1 strain of the virus, farm ministry officials said on Saturday, confirming the second such case in Japan this month.

There have been no reported cases of human infection from the virus in Japan.

Local officials were in the process of culling all 50,000 birds on the farm after 3,200 of them died of the disease. Another 50,000 at an adjacent farm will also be slaughtered as a precautionary measure, a local official said.

Initial tests had shown the chickens on the farm in Miyazaki prefecture were infected with an H5 subtype of bird flu virus, but further testing had been needed to determine whether it was the feared H5N1 strain.

The H5N1 strain is known to have killed 164 worldwide since 2003, most of them in Asia. Some 200 million birds have been killed by the virus or culled to prevent its spread.

Experts fear the virus could mutate into a form which passes easily from person to person, sparking a pandemic in which millions could die.

Later on Saturday, the Japanese Agriculture Ministry said that an outbreak of bird flu was suspected on a farm in Okayama prefecture in western Japan.

Seventeen birds have died on the farm in Takahashi, Okayama, since Friday, an Agriculture Ministry official said. An official at Okayama prefecture said the farm had 12,000 chickens.

"We are doing more detailed tests, and nothing is determined until then," the Agriculture Ministry official said.

Earlier this month, Japan suffered its first outbreak of H5N1 bird flu in poultry in more than three years, also in Miyazaki, the country´s biggest poultry producing region.

Cases of the virus have flared up across Asia in recent weeks, as in previous winters, taking the death toll in Indonesia to 63, the country hardest hit in terms of fatalities.

A 14-year-old boy in Azerbaijan has been sent to hospital as a suspected case, while Vietnam is trying to control the spread of the disease among birds in the Mekong Delta.