BEIJING, Jan 8 (Reuters) - China's Agriculture Ministry said on Thursday that it had found no bird flu cases amongst poultry in Beijing or areas surrounding the city after a woman in the capital died of the H5N1 form of the virus.

Experts had fanned out to Beijing's neighbouring city of Tianjin and Heibei province, which surrounds the capital and where the dead woman had bought ducks, the ministry said in a statement on its website (www.agri.gov.cn).

"After tests for the virus and an epidemiological investigation, no trace of the bird flu virus was found in these three areas," it said.

The 19-year-old died of the H5N1 virus after gutting ducks, which experts say highlights the role and risks of waterfowl in the transmission of the virus to humans.

It was the first such death in the country in almost a year, and the 21st to date in China.

The virus is generally more active during the cooler months between October and March, although the new Chinese case points to holes in surveillance of the virus in poultry.

Experts also say that many species of ducks are natural reservoirs of the virus and unlike chickens, they show no signs of disease.

China's Agriculture Ministry said it would step up an inoculation campaign and surveillance for the disease.

"The ministry has many times demanded that every part of the country must maintain a high state of alert to prevent the spread of bird flu and other animal viruses," it said.

The H5N1 strain remains largely a disease among birds but experts fear it could change into a form that is easily transmitted among people and kill millions of people worldwide.

With the world's biggest poultry population and hundreds of millions of farmers raising birds in their backyards, China is seen as crucial in the global fight against bird flu. (Reporting by Ben Blanchard; editing by Ralph Boulton)

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