The death toll from a new strain of bird flu in China has reached 20, with dozens infected, state media reported Sunday, as experts said there was no evidence so far of human-to-human transmission.

The H7N9 virus has been detected in 102 people, mostly in eastern China, including 20 cases which proved fatal, Xinhua news agency said after the latest daily update from the National Health and Family Planning Commission.

A total of 33 infections, including 11 deaths, have been reported in the eastern commercial centre of Shanghai.

The Chinese Center for Disease Control and Prevention had earlier said 40 percent of patients with H7N9 had not come into contact with poultry, raising questions about how people are becoming infected.

It also emerged that the virus had spread among family members in Shanghai, raising fears that it was passing between humans.

But the World Health Organization (WHO) has said there was "no evidence of ongoing human-to-human transmission".

Referring to those cases on Friday, WHO representative Michael O'Leary said investigators were trying to determine whether there had been human-to-human transmission between family members.

"The primary focus of the investigation is to determine whether this is in fact spreading at a lower level among humans. But there is no evidence for that so far except in these very rare instances," he said.

A team of international health experts is on a week-long mission in Beijing and Shanghai to investigate the virus, for which no vaccine currently exists.

Taiwan said Sunday it had received H7N9 specimens from China as the island battles to avoid the epidemic.

"The virus could be used in producing vaccines and diagnosis," said Liu Shih-hao of the Centers for Disease Control in Taiwan.

Since China announced nearly three weeks ago that it had found the strain in people for the first time, almost all of the cases have occurred in Shanghai and four nearby provinces while one appeared in Beijing.

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