Chinese officials, speaking through the state media on Monday, said they had rushed three million doses of bird flu vaccine to Qinghai province in China's far west.
Officials said scientists determined more than 150 migratory geese found dead had contracted the H5N1 flu virus, the same strain that has killed 54 people in Vietnam, Thailand and Cambodia over the past two years.
Spokeswoman Maria Cheng of the World Health Organization's Beijing office says at this time, the virus seems to have affected only animals and there are no human infections reported. However, she says the organization is monitoring the situation.
"It heightens our concern about avian influenza," said Ms. Cheng. "China hasn't had any reports of avian influenza since last July, so the fact that it's been detected now obviously raises our concern and indicates to us that it's still circulating in the region."
Parts of China are in the midst of the flu season, and Ms. Cheng says that means the elements for a major outbreak are present.
"You have a circulating avian influenza and human influenza, so if these two were somehow to re-combine in a form that is more transmissible among humans, that would set off a pandemic and that's ultimately what we're most concerned about," she added.
So far, almost all human victims of H5N1 contracted the virus from infected poultry. The most recent human death from the disease was announced Monday in Vietnam, where a 46-year-old man became the country's 18th fatality since December.
The government says it has closed off nature reserves and ordered farmers in Qinghai to vaccinate their birds.
Officials are concerned that if the virus spreads from wild birds to farm-raised chickens and ducks, the economic consequences could be devastating. China has the world's second largest poultry industry after that of the United States. When the virus first re-appeared in Southeast Asia in 2003, tens of millions of domestic chickens, ducks and geese had to be killed to halt its spread.