Twelve people have been killed by H7N9 bird flu in a single Chinese province this month, state media reported on Monday, as infections from the virus see a seasonal spike.

The deaths were recorded in the eastern province of Zhejiang, the official Xinhua news agency said, citing local health authorities.

The report came as China was said to have dropped its previous description of H7N9 bird flu as "infectious" in new guidelines on how to deal with the disease.

The National Health and Family Planning Commission described it as a "communicable acute respiratory disease" in its 2014 diagnosis and treatment protocols.

In the 2013 version it was considered an "infectious disease".

The Beijing Times on Monday quoted an unnamed Beijing disease control centre official saying that health authorities decided to "downgrade" the virus on the basis that nearly a year of analysis had shown H7N9 was "not strongly infectious".

But Xinhua reported on Monday that China has banned live poultry trading in the cities of Hangzhou, Ningbo and Jinhua in Zhejiang province.

"The province has launched emergency surveillance of poultry farms, haunts of migrant birds and parks, in addition to halting the flying of domestic pigeons," the agency reported.

The nearby city of Shanghai will also halt live poultry trading between January 31 and April 30, it added.

The H7N9 human outbreak began in China in February 2013 and reignited fears that a bird flu virus could mutate to become easily transmissible between people, threatening to trigger a pandemic.

The guidelines come as human cases undergo a seasonal spike, with 96 cases confirmed in China so far this year, leading to 19 deaths, according to the Chinese Center for Disease Control and Prevention as cited by Xinhua.

More than half have been in Zhejiang, with 26 new cases in Guangdong in the south.

That compares with 144 confirmed cases, including 46 deaths, in the whole of 2013 according to official statistics.

On Monday, the southern Chinese city of Hong Kong said it will cull approximately 20,000 chickens after discovering the H7N9 avian influenza virus in a batch of poultry imported from mainland China.

Improved detection?

It was not clear whether the rise in reported cases is due to the virus becoming more widespread and possibly less severe, or detection and treatment improving.

Cases and deaths had dropped significantly after the end of June, but have begun to pick up with the onset of winter.

"So far, most cases have been sporadic and there were some cluster outbreaks among family members," the commission said in the guidelines.

"But there is no evidence of sustained human-to-human transmission yet," it said, although it added that "limited" and "unsustained" infections could not be ruled out.

China has been accused of trying to cover up disease, particularly Severe Acute Respiratory Syndrome (SARS), which killed about 800 people around the world in 2003.

The World Health Organization (WHO) has more recently praised its openness and response to the outbreaks of bird flu.

WHO spokesman Gregory Hartl told AFP: "There's been an increase in the number of cases, not deaths. The deaths haven't increased that much.

"This is winter, and all influenza viruses disseminate much more easily, much more widely, in winter, so it is not unexpected to see more cases," he said.

The health commission guidelines shortened the disease's incubation period from seven days to three to four days, and the Beijing Times said hospitals would reduce quarantine time for suspected exposures accordingly.

The health commission also inserted the phrase "particularly the elderly" in its description of those vulnerable to the virus -- those who have had contact with poultry or have been to a live poultry market in the week before showing symptoms.