Shimane Prefecture began Tuesday to cull some 23,000 chickens at a poultry farm on suspicion of bird flu cases, local media reported. The move came after five chickens, which were found dead at the farm in the southwestern prefecture on Monday, tested positive for bird flu in preliminary tests. And the birds were suspected of being infected with the highly virulent H5 strain of avian flu virus. Local authorities said the culling operation at the farm in the city of Yasugi is expected to take two to three days. Vowing to contain the spread of the virus, Prime Minister Naoto instructed officials to do their utmost for 'domestic crisis management.' And the central government has set up a task force to deal with the possible outbreak. Shimane and neighboring Tottori prefectures on Tuesday conducted checks on about 40 farms in Shimane and about 90 farms in Tottori with a total of about 4 million chickens. And Tottori prefecture has started disinfecting vehicles on main roads near the affected farm in the city, which borders Tottori. If the bird flu cases are confirmed, it will be the first infection since February 2009 when quails at a farm in Aichi Prefecture were found to be infected by avian flu virus. 