China has for the first time reported human cases of avian flu. The country has begun vaccinating hundreds of millions of chickens and ducks in areas hard hit by the bird flu virus known as H5N1, and plan to vaccinate billions more, in an effort to prevent more human cases.

Chinese authorities late Wednesday said they had confirmed three human bird flu infections, two in Hunan province in central China and one in Anhui, in the country's east. They are the first confirmed cases Beijing has reported.

Official Chinese media did not identify who the patients were.

News reports said the World Health Organization (WHO) office had confirmed that two of the victims, a 12-year-old girl in Hunan and a female poultry worker in Anhui, died. The girl's nine-year-old brother also contracted the disease, but recovered.

Live chickens for sale this week at a market in eastern city of Suzhou

The WHO is working closely with health officials around the world to try to prevent the spread of the H5N1 avian virus to humans. In almost all human cases thus far, transmission has been from birds to people. Scientists fear the virus could mutate and become passable from human to human, possibly leading to a worldwide pandemic.  Roy Wadia, a WHO spokesman in China, warns that the more cases there are, the higher the risk of a dangerous mutation.

"Anytime you have an outbreak in poultry and you've got a large population in close contact with that poultry and there's a chance of even one person being infected, there is this theoretical chance that it could at some point change in a way that it might then become more effective in terms of human-to-human transmission," he said.

H5N1 has killed more than 60 people since it reappeared in Asia two years ago, nearly half of those who contracted the virus.

Over the past several weeks, China has reported at least 11 outbreaks of the virus among poultry flocks in several provinces.

Chinese officials have sought to reassure the public they are doing everything to prevent the disease from spreading among humans. This week, they ordered the vaccination of all of the country's five billion poultry. Authorities in northeastern China's Liaoning province, one of the country's hardest hit, said on Wednesday that 320 million had already been immunized.

The job is gigantic. China has a third of the world's poultry stock, and the country consumes 14 billion ducks, chickens, geese and other birds each year. 

Chicken for sale in Suzhou

At one of Beijing's public markets, a chicken vendor laughs when a reporter asks her whether she thinks the government will succeed in vaccinating all of the country's poultry. 

"I don't know about that. Chicken is the cheapest meat in China right now. The farmers are the ones who suffer most. They're losing money. They have all these chickens and nobody wants to buy them," she said.

While many people say they are heeding government recommendations to cook the meat thoroughly, many are choosing to not buy it at all.  Shoppers in Beijing markets say the price of chicken has tumbled by almost half.