Japan's agriculture ministry says bird flu is spreading at an unprecedented rate across the country this season, hitting new highs in terms of both the number of outbreaks and the scale of birds culled.

The ministry says 76 outbreaks have been confirmed at poultry firms and elsewhere in 25 prefectures since the first cases were reported in October last year. Nearly 15 million birds have been culled so far.

The October outbreaks, in Kurashiki City, Okayama Prefecture, and Atsuma Town in Hokkaido, were the earliest on record to be confirmed in a season.

The flu virus is carried by migratory birds wintering in Japan. The flu usually breaks out from autumn to spring, but infected birds are said to have arrived earlier than usual this season.

The ministry warns that risks are increasing throughout in Japan. This season, the avian flu spread in six prefectures that had never seen outbreaks before, such as Yamagata and Okinawa.

The number of birds destroyed rose as the disease hit large chicken firms, including one in Misawa City, Aomori Prefecture. About 1.39 million birds were culled there in December.

Ministry figures show that the number of culled birds now stands at 14.78 million, about 50 percent more than the 9.87 million recorded in the 2020-21season.