If bird flu is confirmed in any of the three, it would be China's first reported human case. The H5N1 virus has killed at least 62 people across Southeast Asia.
Three people living in central China's Hunan province came down with pneumonia last month following an outbreak of bird flu among local poultry, the official Xinhua News Agency said.
Of those, a 12-year-old girl died. Her nine-year-old brother and a 36-year-old middle school teacher recovered from the illness. At the time, Chinese officials said initial tests showed that the girl and her brother did not have the virus.
But on Sunday, Xinhua said experts cannot rule out the possibility of human transmission of H5N1 bird flu. The agency said needs further laboratory tests to determine the specific cause.
China has asked the World Health Organisation for help in testing blood and throat swabs from the three victims, Xinhua reported.
Roy Wadia, a WHO spokesman in Beijing, confirmed that China approached the agency for help last week. He did not give a specific date.
Public health threat
"This is a reiteration of how much of a public health threat bird flu really is," said Wadia.
"Sometimes it takes a human case or a suspected human case to raise the alarm, to remind us that no country - whether China or anywhere else - can afford to be complacent"
"Sometimes it takes a human case or a suspected human case to raise the alarm, to remind us that no country - whether China or anywhere else - can afford to be complacent."
Wadia said China and the WHO were still working out the details of their cooperation. Samples might be sent to a WHO lab or WHO experts could be asked to help Chinese officials perform the tests in China, he said.
China, which was heavily criticised during the 2003 outbreak of severe acute respiratory syndrome for initially covering up the illness, has pledged it will be more open about reporting on bird flu.
"I think the information they have shared with us has been shared as soon as they can corroborate it," he said.
Wadia also said it was not unusual for someone thought to be infected with a virus such as H5N1 to initially test negative but later to test positive.
The girl, He Yin, who came into "close contact with sick birds", died on 13 October, three days after developing a high fever, Xinhua said. Her younger brother was hospitalised with similar symptoms but recovered.
The third suspected victim was a 36-year-old middle school teacher who reportedly fell ill after chopping raw chicken while suffering from a minor injury to his hand, Xinhua said. The agency identified him only by his surname, Song.
All three lived in or near Wantang, a village where the government says 545 chickens and ducks died of bird flu last month.
Also on Sunday, 1700 officials and 100 police finished culling about 370,000 birds in northern China's Liaoning province after bird flu killed 8940 chickens there.
The outbreak in Liaoning's Badaohao village, east of Beijing, was China's fourth reported outbreak in three weeks.
China has seen outbreaks of bird
flu across the country
Xinhua said late on Saturday that Badaohao lies along a migration route used by migratory birds heading from East Asia to Australia, contributing to fears that wild birds could spread the disease.
More than 20 magpies and other migratory birds had been spotted in the area, it said, without giving further details.
The Chinese authorities have said they are concerned that wild birds might spread the virus, particularly following an outbreak last spring that killed more than 6000 migratory geese and gulls at northwestern China's Qinghai Lake.
Also on Sunday, the government took action to prevent the production and distribution without approval of bird flu vaccines for poultry.
China suffers from rampant
The government revoked the production licences of 60 veterinary drug-makers since January and punished 13 domestic institutions for irregularities related to the production and sale of bird flu vaccines, Xinhua reported, without giving details, citing an unnamed Ministry of Agriculture official.
China's state television news announced a list of nine companies approved by the Ministry to Manufacture and sell any of four approved bird flu vaccines. It warned consumers not to buy vaccines that had not been approved.
China suffers from rampant and sometimes dangerous product piracy. Bogus medicines that have none of the declared ingredients on the packaging are common.
Under new regulations on Sunday aimed at achieving a 100% bird vaccination rate in the capital, anyone who fails to immunise their birds faces up to 15 days in prison and a 200 yuan ($25) fine, the Beijing Morning Post reported.