The World Health Organization says no evidence has emerged to show that a type of bird flu which has killed two Chinese men can be transmitted between people.
Two men in Shanghai, aged 87 and 27, fell sick in late February. A woman in Anhui province also contracted the virus in early March and is in critical condition.
"At this point, these three are isolated cases with no evidence of human-to-human transmission", the WHO representative in China, Dr. Michael O'Leary, told reporters on Monday.
China's National Health and Family Planning Commission confirmed on Sunday that the three cases were the H7N9 virus, which had not previously been known to infect humans.
"A new virus tends to be more virulent in the beginning. Either it is going to become a truly human virus, in which case we have to start dealing with it regularly, or it is going to be primarily an animal virus with just a rare human case," O'Leary said.
Some Chinese had complained that authorities took too long before announcing the deaths on Sunday. O'Leary said the government acted properly as the deaths needed to be investigated.
"China actually for a long time has been reporting promptly and openly. I think SARS was a turning point globally for that sort of thing. Not just in China," he said.
He was referring to the 2003 epidemic of Severe Acute Respiratory Syndrome, which caused a scandal when official numbers of cases were later dramatically revised upwards.
SARS emerged in China and killed about a tenth of the 8,000 people it infected worldwide.
People buying poultry at a Shanghai market on Monday said they were worried the incidents had been made public only weeks after the deaths and said they hoped the government would be quick to report any new cases.
"In the future, no matter what it is, the government should make it public quickly and let the people know early. That way they can prevent it themselves", said shopper Zhang Zhili, 60.
Many users of Chinese microblogs, known as "weibo", said they suspected the latest outbreak of bird flu was related to more than 16,000 pig carcasses recently found dumped in rivers around Shanghai.
O'Leary said that while the dead pigs were part of the overall investigation, there was no evidence of any connection.
It is not known how the three victims were infected. The virus does not seem highly contagious because no health abnormalities were detected among 88 of the victims' close contacts, the health commission said.