The highly pathogenic H5N1 virus is endemic in poultry across Asia, where it is known to have infected 124 people and killed 64. Millions of birds have been culled.

Although H5N1 has yet to be transmitted between people, experts fear it could mutate into a strain that can move easily from person to person, touching off a pandemic that could kill millions.

Migratory birds have spread the disease into eastern Europe and on Friday Kuwait said it had found H5N1 in a flamingo. It was the first known case of bird flu in the Gulf region.

The Thai boy is the first human case in Bangkok since a fresh flare-up of the deadly disease there a month ago. The virus has killed 13 Thais since it swept across large parts of Asia in late 2003.

Worried about a possible mutation into a transmittable killer human virus, Japan has drafted plans to tackle an epidemic, including closing schools around infection zones and declaring a state of emergency if an outbreak spread to a wide area.

Asahi Shimbun daily said the government programme assumed that one in four people in Japan would be affected if an outbreak occurred.

The government estimates that between 170,000 to 640,000 people could die and that between 530,000 to 2 million people could be hospitalised, Asahi said.

Japan will also aim to increase stockpiles of the antiviral drug Tamiflu so there will be enough for 25 million people to be treated over five days, rather than just three days under a previous target, Asahi said.

THREAT

Hong Kong is already bracing for an explosion of cases early next year, a Chinese-language daily said on Saturday.

"Spring is the peak season for human influenza. Once the human influenza virus mixes with bird flu, it will pose a big threat," Wen Wei Po said in a front-page story, quoting an unidentified source at the Hong Kong Hospital Authority which manages all the city's public hospitals.

"If bird flu explodes in the community, the first wave will be very severe. It will pose the biggest threat to young people," the pro-Beijing daily said.

Scientists in Hong Kong said H5N1 apparently causes a "storm" of immune system chemicals that overwhelms the patient.

The study, published in the online medical journal Respiratory Research, might suggest that if H5N1 does cause a pandemic, it could disproportionately affect the young and healthy as compared with seasonal flu, which kills many elderly people but few young adults.

Meanwhile, Hong Kong's government said China had confirmed a fresh outbreak of the H5N1 virus in poultry.

"The Health, Welfare and Food Bureau received notification from the Ministry of Agriculture of the Mainland last night, of an H5N1 avian influenza outbreak among poultry in Jingshan country in Hubei province" the Hong Kong government said in a statement on Saturday.

This latest outbreak comes as China is battling to control seven other outbreaks since the beginning October.

China has yet to report a human case of bird flu, although the World Health Organisation (WHO) is helping probe a possible human case in Hunan province, which had an outbreak in October.

The head of the global animal health body OIE hailed the launch of a $1 billion plan to tackle bird flu unveiled by health experts at a WHO meeting in Geneva this week.

Supported by the World Bank, it is aimed at rooting out bird flu among poultry and stopping it from spawning an influenza pandemic.

"The massive commitment by the World Bank should allow countries affected or at risk to benefit from effective veterinary services," Bernard Vallat, director general of the Paris-based World Animal Health Organisation (OIE), told the French newspaper Liberation.