Two men have died in the Chinese city of Shanghai, after contracting a strain of bird flu not previously known in humans, according to officials.
The men, aged 27 and 87, fell ill with the H7N9 strain in February and died some weeks later in March, Xinhua news agency reported.
A 35-year-old woman who caught the virus in Chuzhou, in the eastern province of Anhui, is said to be critically ill.
It is unclear how the strain spread, but the three did not infect each other or any close contacts, officials say.
According to China's National Health and Family Planning Commission, all became ill with coughs and fevers before developing pneumonia.
There is no vaccine against the H7N9 strain, the commission said. It is conducting tests to assess its ability to infect humans.
Another strain of bird flu, H5N1, has led to more than 360 confirmed human deaths since 2003 and the deaths of tens of millions of birds, the BBC reports.
The World Health Organisation says that most avian flu viruses do not infect humans and the majority of H5N1 cases have been associated with contact with infected poultry.