Chickens were slaughtered during the last outbreak

A strain of the disease killed six people in the territory in 1997.

Authorities said the boy has recovered from the H9N2 strain of the virus after falling ill with a fever, cough and runny nose last month.

He was admitted to hospital on November 27, and discharged two days later.

The alert comes just months after Hong Kong was declared free of Sars, which killed 299 people in the territory, and infected nearly 1,800.

Dr Thomas Tsang, of the Hong Kong department of health said: "This is an isolated case and the source of infection is being investigated.

"Based on previous experience, however, we will look especially into bird-to-human transmission.

"This is the second time H9N2 viruses, an avian influenza virus, have been isolated from humans in Hong Kong.

"The last case was detected in 1999 involving two girls who also made full recovery after having flu-like symptoms."

The H5N1 strain of avian flu, which is carried by poultry, leapt the species barrier to claim six lives in 1997, prompting authorities to order the slaughter of the territory's entire poultry stock.

Another 860,000 chickens and other birds were destroyed following a second outbreak in February 2002.

Members of the public were warned to avoid contact with live poultry and to maintain high standards of personal health and hygiene.