A SEVEN-YEAR-OLD girl is Beijing's first human case of H7N9 bird flu, local authorities say as China's outbreak of the disease spreads to the capital.

The girl, whose parents are poultry traders, was in a stable condition in hospital, the Beijing health bureau said on Saturday. Her mother and father had been quarantined for observation but had shown no symptoms so far, it added.

She developed a fever, sore throat and headache on Thursday, it said, and her parents took her to hospital.

Samples from her tested positive for H7N9 the following day, and the national disease control centre confirmed the results on Saturday.

Chinese officials announced nearly two weeks ago that they had found the H7N9 strain in humans for the first time, and the girl brought the number of confirmed infections to 44, 11 of whom have died.

All previous cases in the outbreak had been confined to eastern China, hundreds of kilometres from the capital.

Experts fear the prospect of such viruses mutating into a form easily transmissible between humans, which would have the potential to trigger a pandemic.

But the World Health Organisation (WHO) said this week that there was as yet no evidence of human-to-human transmission of H7N9.

Health authorities in China say they do not know exactly how the virus is spreading, but it is believed to be crossing to humans from birds, triggering mass poultry culls in several cities.

The United Nations' Food and Agriculture Organisation (FA0) has said H7N9 shows "affinity" to humans while causing "very mild or no disease" in infected poultry, making finding the source of transmission more difficult.

The Beijing health bureau statement did not say whether the girl or her family members had recently travelled to any of the areas where H7N9 infections have been identified.

But Cheng Jun, vice-director of Ditan hospital, where the girl was being treated, told state broadcaster CCTV: "Ever since the outbreak started in Shanghai we have been making preparations."

Beijing, which has a population of more than 20 million, has already banned live poultry trading and pigeon releases, the health bureau said.

Authorities have also ordered stepped-up surveillance of wild birds in the city and people at risk of infection, such as poultry farmers, transporters and vendors, it added.

Shanghai has had 20 confirmed cases so far and was the first place to halt live poultry trading and cull birds last week, followed by other cities in eastern China.

China has said it expects to have a vaccine ready in seven months but US experts said developing one could take "many months".