MANILA (AFP) - The bird flu virus is "firmly entrenched" in Asia and a pandemic among humans remains possible, a World Health Organization (WHO) expert warned Wednesday.

While Asian countries are more prepared to react to any outbreaks than before and have vaccine stockpiles, deaths and infections have continued, noted Takeshi Kasai, the WHO's regional adviser in communicable disease surveillance and response unit.

"The virus has been firmly entrenched in this region, I'm afraid," Kasai told reporters during an exercise to test the Philippines' preparations against the disease.

"The virus itself keeps changing, so the risk of pandemic persists."

Experts fear the virus, which is usually spread directly from birds to humans, could mutate into a form easily transmissible between people, sparking a deadly global pandemic.

Three people have died in China this year of bird flu while a boy and his father were admitted this week to a hospital in Indonesia on suspicion of having the disease.

Since the first human cases were reported in 2003, at least 200 people have died from the H5N1 virus around the world, the WHO said. Indonesia is the world's worst-hit country, with 11 deaths so far this year.

Brunei, Singapore and the Philippines remain the only countries in the region where the flu, either in birds or humans, has not been detected.

Kasai praised China for being more transparent in reporting suspected cases.

"I think China now is very open and has been positively sharing information, including lab results," he said.

China has been highly criticised in the past for withholding information relating to the spread of Severe Acute Respiratory Syndrome (SARS) that ravished the region several years ago.