Authorities began culling 310,000 chickens at a farm on the Sea of Japan coast early Tuesday after a highly pathogenic strain of H5 avian influenza was detected in five birds, local authorities said.

The government confirmed that the highly virulent H5 strain was detected in birds at a chicken farm in Niigata, where about 40 of them were found dead Monday. Dead ducks at a farm in another prefecture of Aomori also tested H5 positive.

Culling of about 310,000 birds began Tuesday at the Niigata farm and will continue through Friday. Workers in hazmat suits dug holes and dumped dead birds in them to contain the spread of virus. About 165,000 ducks in Aomori were also being culled

Authorities in Niigata and Aomori decided to restrict the movements of poultry and eggs within 3 kilometres of the farms in question.

Environment Minister Koichi Yamamoto told reporters that his ministry is sending experts to the areas for investigation, while raising the caution level to the highest level. The Agricultural Ministry has also dispatched an investigative team to both prefectures.