A girl of seven is being treated in hospital in Beijing, in the first case of H7N9 "bird flu" reported by Chinese officials in the capital.
The child, whose parents are poultry traders, developed a fever, sore throat and headache on Thursday. Her condition is said to be stable.
Two people in close contact with her were quarantined for observation but have shown no symptoms so far.
The UN had recorded 28 cases and nine deaths in China as of Wednesday.
There are no reported cases outside the country, according to the World Health Organization (WHO).
China's national disease control centre confirmed on Saturday that the girl take ill in Beijing had the H7N9 virus.
The first cases of the virus were reported in February, in eastern China. According to the WHO, there is no evidence that the H7N9 virus is being transmitted between people, and most cases come from poultry.
International health experts have commended China on its transparency in reporting the spread of the virus, in sharp contrast to its handling of a Severe Acute Respiratory Syndrome (Sars) outbreak in 2003, when 8,096 people were infected worldwide and 744 died.