While there is little immediate threat to humans from the infected birds, the discovery revives concerns that the disease could still be a problem with poultry flocks in southern China -- although it isn't yet clear whether the infected birds came from local or mainland Chinese farms.
Hong Kong authorities said they have reported the incident to their mainland counterparts and are sending experts to inspect mainland farms. York Chow, Hong Kong's secretary for food and health, said Saturday the government was stepping up inspection of the city's 64 poultry markets.
"If we find another positive detection in another market, then we will assume that the risk is much higher and we need to cull all the chickens in all the markets," he said.
Liu Haitao, an official with China's Ministry of Agriculture, said the H5N1 virus hasn't been found in any chickens in mainland China.
"We have been inspecting and preventing," Mr. Liu said, adding that if authorities discover any cases they would make them public in a timely manner.
An official with China's General Administration of Quality, Supervision, Inspection and Quarantine said the agency needed to consider questions about the matter before responding.
Hong Kong officials declared the affected market, in the Sham Shui Po district of the city, an infected area. Traces of the virus were detected in five of 20 samples of chicken waste collected from three stalls there.
"In the past three or four years, we haven't detected any cases of H5N1 in a Hong Kong poultry market, so this is a bit unusual," said Yi Guan, a professor of microbiology at Hong Kong University.
Prof. Guan said it would take a few days of laboratory testing before scientists have a clear idea of the virus's source and its potential danger to humans. "Each virus has its own genetic mark, and based on this mark, we can basically understand whether this virus is a new one or old one, and what region it comes from," he said.
Scientists warn that mutations in the H5N1 strain of avian influenza could potentially create a global pandemic threatening millions of human lives. So far, the disease's impact has been muted by its inability to easily pass from human to human. Since 2003, it has infected 383 people in 15 countries, including China, Indonesia and Vietnam, according to the World Health Organization. Of those confirmed cases, 63% have proved fatal.
Hong Kong has seen occasional incidents of H5N1 but no major outbreaks since 1997, when an outbreak killed six people and led to a slaughter of about 1.5 million birds.
