80,000 birds culled; poultry farms closed; mainland imports halted Hong Kong was on alert last night after the dreaded bird flu was found at a farm in Yuen Long. The government immediately shut down all poultry farms and markets, culled 80,000 chickens and halted imports of mainland chickens. The H5 virus killed 200 chickens at the farm, sending the government scurrying to find out what went wrong with its much-vaunted anti-bird flu control programme. As results of tests to confirm if the bug is the deadly H5N1 strain were awaited, questions were being raised over whether the virus had mutated or the Dutch-made vaccine being used on local chickens had failed. Of particular concern is the fact that the dead chickens included vaccinated as well as unvaccinated birds. All 68,000 birds on the affected farm - owned by New Territories Chicken Breeders Association secretary Wong Yee-chuen, in Lau Fau Shan, Yuen Long - were killed, together with 12,000 chickens at a nearby uninfected farm. About 10,000 chickens at the Cheung Sha Wan wholesale market will be culled from today. All wet markets will be closed even though they have shown no signs of infection. The Aviary Pagoda in Yuen Long Park has also been shut indefinitely. The outbreak comes seven months after the poultry trade was shut down following the discovery of the virus in wet markets. The overnight keeping of live chickens at markets was banned following the outbreak in June. The last outbreak on farms, in 2003, led to vaccination of chickens. Secretary for Food and Health York Chow Yat-ngok declared a 'serious alert', which means a 21-day shutdown of the trade - until December 29 - unless there is another outbreak. He expressed concern that both 'sentinel' and vaccinated birds had died since the first death at the farm on Monday. 'The first deaths ... were sentinel chickens - those not vaccinated,' he said. 'After the outbreak, we found more vaccinated chickens were also affected.' Dr Chow said the source of the virus was also a concern. 'The virus exists in the natural environment in wild birds. Whether there is any biosecurity lapse in the farm or any contamination of some of the things inside the farm will require further investigation,' he said. The head of microbiology at the University of Hong Kong, Yuen Kwok-yung, called on the government to consider using mainland H5N1 vaccines at Hong Kong farms. 'Perhaps the Hong Kong government can talk to the mainland manufacturer to see if it can produce vaccines that can target H5N1 strains found in Hong Kong. It is one of the possibilities,' he said. Agriculture, Fisheries and Conservation Department assistant director Thomas Sit Hon-chung said the department had been using the same H5N2 vaccine from the Dutch company Intervet for five to six years. Mr Wong said it was the first time his farm had been infected. 'Because my farm is so big, I am stringent in the measures ... I do not understand why there is still an outbreak,' he said. Mr Wong and six farm employees, three of them women, were taken to Princess Margaret Hospital for check-ups yesterday. The Centre for Health Protection said they would be kept under observation. The discovery of the first dead bird on Monday came after a batch of chickens from the farm was declared virus free on Friday and sold in the wholesale market. Xinhua said last night that border controls would be stepped up.