A total of 31 people died from H7N9 bird flu in mainland China in January, the government announced Monday, making it by far the worst month in the outbreak.

There were a total of 127 confirmed human H7N9 cases in January, according to a statement by the National Health and Family Planning Commission (NHFPC).

The number is almost as high as for the whole of last year, when China had 144 confirmed cases including 46 deaths.

Flu viruses are seasonal and the first human cases emerged in February 2013, so that the outbreak did not encompass all of last winter.

It has reignited fears that a bird flu virus could mutate to become easily transmissible between people, threatening to trigger a pandemic.

But NHFPC spokesman Yao Hongwen told a press conference: "So far the features of human infection of the H7N9 bird flu have not had obvious changes and most cases remained sporadic.

"Our monitoring has not found any... mutation in the virus and the way the virus spreads remains poultry-to-human."

The World Health Organisation also says there is no evidence of sustained human-to-human transmission.

Chinese researchers are developing vaccines for the disease and one has passed a safety test on animals, Yao added.

But according to reports clinical trials in humans have yet to begin.

According to an AFP tally of local government announcements, so far there have been at least 180 cases reported this year, including 33 deaths.

Zhejiang province in the east and the southern province of Guangdong are the worst affected, reporting 77 cases and 54 cases so far respectively, the tally showed.

China's traditional and popular live poultry trade should be replaced by frozen meat distribution to reduce the risk of H7N9 bird flu infection, said Shu Yuelong, director of China's national flu centre.

Live poultry markets are common in China and elsewhere in Asia, and present an ideal environment for virus spread between birds kept together in very high concentrations.

Zhejiang has said that such facilities will be closed in the province's major cities and affected smaller towns for three months by February 15, and permanently in major cities from July 1.