This will be the seventh outbreak of avian influenza in Japan and the third this year if the outbreaks of the H5N1 strain reported this month at two farms 60 km apart in Miyazaki Prefecture are confirmed to be separate cases.

Before this year's outbreaks, four cases of bird flu were reported in Japan between 2004 and 2005.

Further laboratory work will be conducted at the National Institute of Animal Health to determine how virulent the detected virus is and if it is the lethal H5N1 strain, with results expected in a matter of days, the ministry said.

The Agriculture, Forestry and Fisheries Ministry also plans to have its task force investigate the infection route which has so far been untraced, ministry officials said.

At the Hashimoto Nojo farm in Takahashi city, 10 chickens were found dead Monday, following reports of the deaths of two birds on Friday, 20 on Saturday and 17 on Sunday, bringing the death toll there to 49, the Okayama prefectural government said.

Under the Domestic Animal Infectious Disease Control Law, the local government will gas from Tuesday some 12,000 chickens the farm has been raising in eight poultry houses for eggs, its officials said.