TOKYO, Nov. 29 (Xinhua) -- Niigata, a central prefecture of Japan, began culling about 310,000 chickens on Tuesday at a poultry farm where highly pathogenic bird flu strain had been detected.

About 40 chickens at the farm were found dead Monday. All five chickens sent for a preliminary test were found positive for bird flu, and further tests confirmed the presence of a highly contagious strain.

Bird flu cases were also found in Aomori prefecture in northeastern Japan. Nine ducks at a farm tested positive for H5 strain of virus, though it is not clear yet how pathogenic the cases were.

The governments of Niigata and Aomori have ordered farms within 10 kilometers of the poultry farms in question to stop transporting eggs and poultry out of the areas.

About 60 farms are keeping about 500,000 birds within a 10-km radius of the farm in Niigata and 7 farms keep over 400,000 birds in Aomori, according to local reports.

Japanese Prime Minister Shinzo Abe has instructed relevant government ministries and agencies to coordinate to deal with the matter.

Japan's environment ministry has recently raised the country's bird flu alert to the maximum level 3, as highly pathogenic H5N6 strain has been found in wild birds in multiple prefectures.