A highly virulent strain of H5 avian influenza was detected at the farm in Joetsu City after about 100 chickens died between Tuesday and Wednesday, the Niigata prefectural government said.

The local government restricted movements of poultry and eggs in areas near the farm.

On Tuesday, authorities started to destroy about 310,000 chickens at a poultry farm in Sekikawa Village, 140 kilometres north-east of Joetsu, after some of them tested positive to the H5 bird flu strain.

In the northern prefecture of Aomori, more than 18,000 ducks were culled at a farm after tests indicated the presence of the H5 bird flu strain there.

Japan to cull a further 230,000 chickens after bird flu outbreak

Tokyo - About 230,000 chickens will be killed at a poultry farm on the Sea of Japan coast Thursday after an outbreak of bird flu was confirmed, authorities said.