China's H7N9 bird flu spread west to the central province of Henan on Sunday, as government websites and state media reported two deaths and 11 new cases nationwide.

The new strain of the flu had been confined to the eastern city of Shanghai and nearby Zhejiang, Jiangsu and Anhui until Saturday when the first case was reported in Beijing.

In total 60 people have been infected and 13 have died of the disease since Chinese authorities announced two weeks ago they had found H7N9 in humans for the first time.

Two new cases were reported in Henan on Sunday by Xinhua state news agency, as government websites also announced four new instances in Zhejiang, two in Jiangsu and three in Shanghai along with two deaths in existing cases.

Nine of the 11 new victims were male and seven of them were in their sixties and seventies.

The Beijing-based patient was the seven-year-old daughter of poultry traders and her condition had improved.

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 Organization (WHO) said last week there was as yet no evidence of human-to-human transmission of H7N9.

The close contacts of the victims reported on Sunday were under observation but none were reported so far to have displayed abnormal symptoms.

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

Beijing has halted poultry trading and banned the flying of pigeons, China National Radio reported on Sunday.

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

In 2003 Chinese authorities were accused of trying to cover up the outbreak of Severe Acute Respiratory Syndrome, which went on to kill about 800 people worldwide.

But China has been praised for transparency over H7N9, with the WHO saying it was pleased with the level of information sharing and US scientists congratulating it for "the apparent speed with which the H7N9 virus was identified" in a New England Journal of Medicine article.

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