SHANGHAI (AFP) - Three members of the same Chinese family have contracted H7N9 bird flu in the province worst-affected by the current spike in cases, the official Xinhua news agency reported.

A couple and their daughter in Hangzhou, the capital of the eastern province of Zhejiang, were infected one after another, Xinhua said late on Tuesday, without giving further details.

Health authorities are investigating, it added.

China's human H7N9 outbreak began in February 2013 and sparked fears the virus could mutate to become easily transmissible between people, potentially triggering a pandemic.

Both Chinese authorities and the World Health Organisation have said there has been no evidence so far of sustained human-to-human transmission.

But limited spread, such as between relatives in close contact, is possible, and there have been previous such family clusters.

So far this year, China has confirmed 110 human H7N9 cases, including 22 deaths, according to an AFP tally of reports by local authorities.

Zhejiang alone has seen 53 cases, almost half the national total, and 12 deaths.

Local authorities are to permanently ban live poultry markets in major cities, according to reports in official media.

For last year as a whole, China had 144 cases, including 46 deaths, from H7N9 avian influenza, according to figures from China's National Health and Family Planning Commission.