Shanghai's live poultry markets were shut on Saturday as another Chinese city culled birds to prevent the spread of H7N9 avian influenza, which has killed six people in the country.

China has confirmed 16 cases of the H7N9 strain since announcing a week ago that the virus had been found in humans for the first time.

The cases have been confined to eastern China, with commercial hub Shanghai recording six including four deaths, and the other two fatalities in the neighbouring province of Zhejiang.

One Zhejiang victim had eaten quail bought at a market in Hangzhou, the provincial capital, at which authorities began culling birds on Saturday after finding quail infected with H7N9, the official Xinhua news agency said.

In Shanghai, a uniformed worker sprayed disinfectant from a tank on his back at one local market in the city centre, where two live poultry booths were dark and the cages empty.

"People are worried," said Yan Zhicheng, a retired factory manager who like many elderly people in Shanghai makes a daily trip to market.

"Shanghai people eat a lot of duck and chicken. Now we can't touch them."

Shanghai had culled more than 20,500 birds at an agricultural market in a western suburb by Friday, after the virus was found in pigeons, and the government announced a ban on live poultry trading and markets.

But eggs remained on sale, as well as fresh and frozen poultry meat, as officials encouraged people to cook them well.

Chinese authorities maintain there is no evidence of human-to-human transmission, a conclusion echoed by the World Health Organization (WHO).

The US Centers for Disease Control and Prevention on Friday on warned of the potential risk should the virus mutate.

"This is a 'novel' (non-human) virus and therefore has the potential to cause a pandemic if it were to change to become easily and sustainably spread from person-to-person," it said in a statement.

"So far, this virus has not been determined to have that capability."

The US government on Friday advised American citizens living in China of the cases but said no travel or trade restrictions would be applied to the country based on the current situation.

In Shanghai residents were taking no chances, turning to traditional medicine and donning face masks.

Drugstores were running short of banlangen, a traditional Chinese medicine for colds made from the roots of the woad plant, used as a blue dye from ancient times.

"No one knows what might happen with bird flu, so they are buying it," said a clerk at the Ren Shou Tang medicine store, which had sold out of the medicine's powder form.

The United Nations on Friday drew up a list of recommendations to try to curb the spread of H7N9.

Advice included regular hand washing for those handling birds, keeping animals away from living areas and avoiding eating sick animals.