A chicken farm at Pat Heung was quarantined by the Agriculture, Fisheries and Conservation Department last night after dead chickens tested positive for bird flu. Inspections by AFCD staff found over 160 dead chickens at the farm yesterday. 'As the test showed the samples gave positive results for H5 virus in the evening, the farm was immediately quarantined and the farmer was stopped from selling chickens,' an AFCD spokesman said. 'Most of the remaining 50,000 chickens on the farm are housed in separate sheds from the ones in which the dead chickens were found. These chickens show no clinical symptoms of infection. We have decided to put these chickens under close observation. 'Depending on our observation, we will take appropriate measures to control the spread of the infection.' The farm last delivered chickens to the Cheung Sha Wan Temporary Wholesale Poultry Market on December 20. That batch passed blood tests at the farm and at the poultry wholesale market. The AFCD inspected the farm on December 28 and no abnormal deaths were found at that time. AFCD staff inspected 43 other chicken farms yesterday but found no unusual deaths. Farms near the one quarantined will be placed under close observation in the coming days. 'We remain on full alert and will take appropriate actions as and when required,' the spokesman said. On December 28, 16,000 chickens were slaughtered on a chicken farm in the New Territories and a wholesale market was closed amid rising fears of a widespread bird flu outbreak. The cull at the Ta Kwu Ling farm was ordered after more than 1,000 chickens died there. Tests on 12 chickens from the farm proved positive for the H5 virus. Yuen Kwok-yung, professor of microbiology at the University of Hong Kong, has warned that bird flu could spread with the onset of winter. On December 10, Penfold Park in the centre of Sha Tin racecourse was closed for a month after 31 ducks and geese died of the H5 virus in two weeks. A week later 20 chickens were found dead at a market stall in Mui Wo.