A senior United Nations health official has said bird flu is deeply entrenched in bird populations across Asia and warned that China and other countries have a big challenge on their hands fighting the disease.
Mr David Nabarro, the UN co-ordinator for avian and human influenza, has said up to 150 million people could die in a flu pandemic if the H5N1 virus that causes bird flu mutates into a deadlier form that spreads more easily among humans.
China says the situation will be very grave over the coming months of autumn and winter.
"All countries in this region are facing considerable challenges to do with H5N1-caused influenza," said Mr Nabarro, referring to a strain believed to have killed 67 people.
"These are substantial because the epidemic is really quite deeply embedded into the domestic and industrial bird population."
Mr Nabarro met China's health minister and its chief veterinary officer yesterday, and said he was confident the country was being open about the disease.
He also said China, which reported a new outbreak of bird flu north of Beijing this week, and other countries must stay on the lookout for fresh outbreaks.
"Surveillance has to be extremely widespread and very good," Mr Nabarro told reporters in Beijing. "This is a big challenge. You've got to give the issue a high priority. They've got other issues on their plate that they'll perhaps have to give slightly less priority to."
Chinese officials have said they will fully co-operate with the United Nations in tracking and fighting bird flu. But the country's size and attempts to conceal the Sars epidemic in 2003 have prompted fears among some experts that China has had more cases than officially recorded.