Investigators found 519 dead bar-headed geese and other birds in a nature reserve in the western province of Qinghai, said a report by Jia Youling, director of the Ministry of Agriculture's Veterinary Bureau, to the World Organization for Animal Health. Jia's secretary, who gave his surname as Sun, confirmed the report.

China previously reported 178 birds found dead at the reserve. It ordered all 3 million chickens, ducks and other farm birds in Qinghai vaccinated and told the public to avoid nature reserves.

The Ministry of Health, in a statement issued Thursday, said authorities have found no evidence that the disease spread to humans or domestic poultry.

That followed unconfirmed claims circulating on Web sites that as many as 120 people had died of bird flu.

"We've seen those reports about possible human H5N1 cases, and have requested more information from the Ministry of Health," said Maria Cheng, spokeswoman for the World Health Organization in Beijing.

Cheng said WHO was urging China to share virus samples from the dead birds to allow comparisons with other avian flu outbreaks. The group also is seeking more information on human exposure to the dead birds and on control measures being taken.

"It's important that the virus is shared," said Julie Hall, a WHO expert in Beijing. "We need to know what this virus is. ... And we need to be reassured that the right precaution measures are taken to protect human health."

Said Cheng: "It would be premature to consider this event over."

As a precaution, local health officials in Qinghai have been screening all pneumonia and flu-like cases, setting up a network to share information, and urging local residents to take special precautions, the Ministry of Health said.

Consumption of birds found dead has been banned, it said.

People who had been in close contact with the birds were being closely monitored and authorities were sterilizing areas where the dead birds were found, the official Xinhua News Agency reported, citing local officials.

"All hospitals have been told to set up a task force and put aside medication and facilities for the treatment of any avian flu cases that might be detected," Xinhua quoted Ai Keyuan, an official with the provincial health bureau, as saying.

In a separate report, Xinhua said researchers in northern China have developed two new vaccines capable of preventing the H5N1 strain of bird flu from spreading among birds, animals or humans.

"Experiments show the efficiency rate of the newly developed vaccines in preventing infection by the H5N1 virus is 100 percent, " Chen Hualan, director of the China National Bird Flu Reference Laboratory, was quoted as saying.

The vaccines are reportedly more effective than others in preventing spread of the virus among water fowl. They also reportedly extend immunity to infection among chickens by four months.

The vaccine developed in Chen's lab has been sent to Qinghai and her institute is willing to provide technical help to other countries affected by bird flu, the report said.

However, officials at the World Health Organization's office in Beijing said they believed Chen's research involved only birds, not humans, and that no animal or human clinical trials have been run on the vaccines.

The Xinhua report said China also has developed new technologies that can speed up the detection of the bird flu virus to 10 hours from the 72 hours required in the past.

Speeding up detection of the disease would allow more time for prevention and containment of outbreaks, it noted.