Bird flu has been detected in a fourth Japanese prefecture, the agriculture ministry said on Tuesday, as a wave of infections at poultry farms sparks the country's worst outbreak in more than four years. 

Avian influenza was discovered at a poultry farm in Hyuga city in Miyazaki prefecture in southwestern Japan, the ministry said on its website. There is no possibility that humans will contract bird flu from eating poultry or eggs, the ministry said. 

Japan's worst outbreak since at least 2016 started last month in Kagawa prefecture on Shikoku island, which is adjacent to Kyushu island where Miyazaki is located.

The 40,000 chickens at the Miyazaki farm will be slaughtered and buried, while exports in a 3-kilometer radius around the farm will be restricted. 

The new action means more than 1.8 million chickens will have been culled since the latest outbreak began. 

Japan's last outbreak of bird flu was in January 2018, also in Kagawa prefecture, when 91,000 chickens were culled.