The bird was found dead in Lok Ma Chau in northern Hong Kong on Tuesday and initial tests showed it was infected with a virus from the H5 family of bird flu viruses.

"We need to narrow it down to see if it was infected with H5N1," a government spokesman said told Reuters on Wednesday.

The government would inspect all poultry farms within five km (three miles) of where the bird was found as a precaution, he added.

H5N1 is found in wild birds, some species of which migrate to nature reserves and wetlands in Hong Kong each year to escape the cold northern winter.

They have long been seen as the source of the disease, which was first recorded in humans in Hong Kong in 1997, when it killed six people.

But the virus has since been sporadically found in domestic poultry in the city and is now believed by experts to be endemic in chicken and duck populations in many parts of Asia - which means that wild birds may not necessarily spark any future outbreak.

Concerns over the virus re-emerged after a 16-year-old girl in Vietnam died on Saturday of the disease.

Hanoi is now testing samples from two more suspected bird flu cases, one of whom has died. If confirmed, they would bring the human death toll in Vietnam from H5N1 to 24 since December 2003.