Chinese health authorities said on Monday a 16-year-old boy in central Hunan province is badly ill after contracting the H5N1 birdflu virus, the third case reported in as many days as the Lunar New Year holiday looms.

The Ministry of Health said on its Web site the teenager entered a hospital in Hunan on Jan. 16 and the province disease control center confirmed he was infected with the H5N1 virus.

"The patient's condition is critical," the statement said. It added that he previously had "contact with dead poultry."

China has warned of the risk of further human cases of bird flu in the run-up to the Lunar New Year holiday after reporting two new cases over the weekend.

Until this month, China had not seen a single human infection in almost a year, but it has now confirmed four cases of the H5N1 virus in less than two weeks.

Two have died, one a 27-year-old woman who died in eastern China on Saturday, and the other a 19-year-old woman who died in Beijing earlier this month.

"As the Spring Festival approaches, there are frequent movements of poultry products and the risk rises of virus outbreaks and transmission," the Agriculture Ministry said in a statement on its Web site.

The Spring Festival, or Lunar New Year holiday, starts next Monday, accompanied by a mass movement of people back to their home provinces for lavish celebratory meals.

Hong Kong's top health official, York Chow, called on China to release the results of epidemiological tests into the three cases.

"There are two main areas that we are concerned with. One is if there is no avian flu outbreak in poultry and yet there are human cases, whether there's a change in the virus," said Chow, Hong Kong's secretary for food and health.

He also voiced concern over the possibility of "silently infected chickens" carrying the virus or transmitting the disease without showing outward birdflu-like symptoms.

The World Health Organisation said people must be aware of how to protect themselves from bird flu.

Precautions

During the holiday season, when people are more exposed to poultry as consumption rises, people are urged to maintain normal precautions against avian influenza, such as ensuring all poultry is well cooked and always washing hands after contact with raw meat, it said in a statement.

China said over the weekend that a woman in the eastern part of the country had died and a two-year-old girl was critically ill in the north after becoming infected with bird flu.

State television said on Monday that the girl was in stable condition in hospital though was not yet out of danger. But it added that nobody else she had been in contact with had shown signs of illness.

The latest infections bring China's total to 34 human bird flu cases. At least 22 people have died.

The ministry said there had been no reported outbreaks of bird flu among poultry in the two provinces where the two-year-old patient had lived, and was sending out teams of experts to probe how the virus could have spread.

"The ministry has already asked Shanxi and Hunan provinces to ... strengthen their bird flu prevention work," it said.

Experts have said the new cases are not unexpected as the virus is more active during the cooler months between October and March, but have also pointed to holes in surveillance of the virus in poultry in China.

The H5N1 virus remains largely a disease among birds, but experts fear it could change into a form that is easily transmitted among humans and spark an influenza pandemic that could kill millions of people worldwide.

With the world's biggest poultry population and hundreds of millions of backyard birds, China is seen as critical in the fight to contain bird flu.

Since the H5N1 virus resurfaced in Asia in 2003, it has infected 391 people, killing 247 of them, according to WHO figures released in mid-December.