The deadly H7N9 bird flu strain claimed a new victim on Monday when a hospital patient died in China, state media reported, bringing the death toll from the recently identified virus to 24.

A patient surnamed Chen died in the eastern city of Shanghai after 12 days of medical treatment failed, Xinhua news agency said. China has recorded more than 120 cases of H7N9 infection so far.

Most cases since the new strain was first identified in late March have been confined to eastern China, and the only one reported outside mainland China has been in Taiwan. The Taiwanese victim was infected in China.

But experts fear the possibility of the virus mutating into a form easily transmissible between humans, with the potential to trigger a pandemic.

The World Health Organisation has said there has been no evidence so far of human-to-human transmission but warned that H7N9 was "one of the most lethal" influenza viruses ever seen.

Chinese researchers, reporting in The Lancet on Thursday, said they had confirmed poultry as a source of the virus among humans.

Chinese health officials have acknowledged so-called "family clusters", where members of a single family have become infected, but have not established any confirmed instances of human-to-human transmission.

Most of the cases reported have not yet resulted in death, and some patients been discharged from hospital after apparently recovering.