There is a need to destroy these viruses thoroughly to prevent them lingering in the markets

Lily Yam, Hong Kong Secretary for the Environment and Food

It is the first case of avian influenza in chickens in Hong Kong since 1997.

That was the only known outbreak anywhere, and the infection jumped the species barrier and killed six people.

Hong Kong's Secretary for the Environment and Food said the current strain is not believed to pose a risk to humans.

But the authorities have moved fast in ordering a precautionary cull, and are hoping to avoid a repeat of the previous outbreak.

Virulent strain

The infection is a new, previously undetected one and it is described as highly virulent. In 24 hours, it has killed almost 800 chickens, kept in cages in three separate markets.

Officials hope to contain the outbreak

The markets have been closed and 4,500 birds are being slaughtered.

Hong Kong's Secretary for the Environment and Food, Lily Yam, said gene sequencing tests showed the current strain was different to the one which caused the 1997 outbreak

She said there is no reason for immediate alarm.

"There is a need to destroy these viruses thoroughly to prevent them lingering in the markets... with the probability that they might combine with other viruses to result in a new string which may affect human beings," she said.

Hong Kong's acting Director of Health, Paul Saw, said that the previous outbreak taught Hong Kong a bitter lesson, and he would be extremely relieved if no human cases are found within the next week.