A cull of more than 100,000 chickens was under way at a farm in Yuen Long last night after preliminary investigations revealed bird flu had hit Hong Kong for the third time.
Agriculture officials said further tests would be needed to find out if the influenza virus in the latest outbreak belonged to the H5 strain that killed six people in 1997.
Microbiologists believe that an H5 virus is the culprit because of the high mortality rate and speed of the outbreak.
As workers set about gassing chickens on the farm last night, the poultry sector and medical experts called for more stringent official surveillance of chicken farms after it was revealed that the farm had been inspected on Monday last week and declared free of disease.
Dr Ho Pak-leung, of the microbiology department at the University of Hong Kong, said the signs so far suggested that it could be an H5 virus as chickens died quickly and in large numbers.
The department's director, Thomas Chan Chun-yuen, said yesterday that the vets inspected the farm in Yuen Long on Monday and found its chickens clean of disease. But on Wednesday, the department 'learned' from Cheung Sha Wan Temporary Wholesale Poultry Market that a batch of chickens appeared ill, deputy director Dr Liu Kwai-kin said.
Officials admitted that hundreds of chickens from the farm at the centre of the scare had already been sold to wet markets.