The spread of highly pathogenic avian influenza, commonly called bird flu, has put the poultry industry on alert after previous outbreaks led to the culling of tens of millions of birds. Outbreaks also often lead to trade restrictions.

It is attracting the attention too of epidemiologists as the virus can be transmitted to humans. China has reported 21 human infections with the H5N6 subtype of avian influenza so far this year, more than in the whole of 2020.

South Korea reported an outbreak at a farm of around 770,000 poultry in Chungcheongbuk-do, the World Organisation for Animal Health (OIE) said on Monday, citing a report from the South Korean authorities. All animals were slaughtered.

Also in Asia, Japan reported its first outbreak of the 2021 winter season, at a poultry farm in the northeast of the country, the OIE said, confirming a statement last week by Japan's agriculture ministry. The serotype in this outbreak was H5N8.

In Europe, Norway reported an H5N1 bird flu outbreak in the Rogaland region in a flock of 7,000 birds, the OIE said.

Outbreaks generally occur in the autumn, spread by migrating wild birds.

The Belgian government put the country on increased risk for bird flu, ordering poultry to be kept indoors as of Monday, after a highly pathogenic variant of bird flu was identified in a wild goose near Antwerp.

This followed a similar move in neighbouring France earlier this month and in the Netherlands in October.

Bird flu cannot be transmitted through the eating of poultry products.