In east China's Zhejiang province, seven human H7N9 cases were reported on Friday, bringing the total number of such cases to 44 in the province. All the newly reported cases, aged from 23 to 82, are in critical conditions, according to the provincial health authorities.

To limit spreading of the virus, the Zhejiang provincial capital of Hangzhou called a halt to live poultry trading in urban areas on Friday.

Events such as circuses involving live animals were also suspended, according to a circular released late on Thursday.

Li Lanjuan, a leading researcher on bird flu at the Chinese Academy of Engineering, said the move to close poultry markets was necessary to help human beings avoid contact with infected live poultry.

Many live poultry markets in cities of Jinhua, Ningbo and Shaoxing were also closed.

In another development, scientists with the Institute of Microbiology of the Chinese Academy of Sciences said Friday, based on their research results, that the possibility of human-to-human transmission of H7N9 virus is extremely slim.

"H7N9 virus infects human through respiratory tract, so eating cooked poultry will not be infected," said Liu Yao, one of the scientists.

Scientists said transportation of poultry plays an important role in helping the virus spread. They called for controlling the channel from poultry to human, and sterilizing live poultry markets.