The local administration is to inspect 15 chicken farms within a radius of 30 kilometres of the lake on Wednesday and Thursday, the statement said.

About 42,000 chickens will be subject to the inspections.

'We will see if proper measures, such as anti-bird nets, are being taken to prevent wild birds from entering the farms,' said prefectural health official Takayo Yamaguchi.

In March last year, hawk eagles were found infected with the H5N1 bird flu virus in the mountains of Kumamoto on the southern island of Kyushu.

Japan also reported four H5N1 outbreaks in January and February last year, leading authorities to kill tens of thousands of chickens as a precaution.

The H5N1 strain has killed more than 230 people worldwide, but none in Japan, since late 2003 through contact with infected birds, with about half of the cases in Indonesia.

Health experts fear the strain could mutate into a form easily transmitted from person to person, leading to a pandemic. -- AFP