The Ministry of Agriculture reported on Thursday two new outbreaks of bird flu, one in Xinjiang in the far northwest and the other in the central province of Hubei.
The latest reports bring to 13 the number of outbreaks, across six provinces and regions, confirmed in China over the past month.
The fresh outbreaks followed confirmation on Wednesday night of the nation's first known human cases of bird flu.
The Health Ministry said the virus had killed one woman, likely claimed the life of another girl and infected one boy who has since recovered.
The ministry said a 24-year-old female poultry worker from the eastern province of Anhui, Zhou Maoya, died of bird flu on November 10 after falling ill on 1 November.
China is trying to prevent a bird
A 12-year-old girl, He Yin, from an infected area in neighbouring Hunan province who died on 17 October was also "suspected" to have been a victim of H5N1, the ministry said.
The ministry said that, according to World Health Organisation (WHO) guidelines, He's case could not be definitively confirmed as bird flu because reliable laboratory samples were not available.
However the ministry said He's brother, He Junyao, nine, was infected with bird flu. The boy has since recovered and was discharged from hospital last week.
Health authorities said the siblings fell ill shortly after eating a chicken that had died suddenly.
The WHO, which sent an investigation team to the family's village, confirmed the findings and said more human cases were likely in China, although not a huge number.
"That's always of course possible...as long as there are poultry outbreaks, people will be exposed to the virus. You can expect that people might get infected," WHO's China head, Henk Bekedam, told reporters in Beijing.
"On the other hand, I would like to stress...the current virus is not easily transmittable to humans. We don't expect a large number of cases."
Other cases of H5N1 crossing from birds into humans in China were also being investigated on Thursday.
In northeastern Liaoning province, a poultry farmer who had contracted pneumonia after coming into contact with dead chickens was being investigated despite initially testing negative for the virus and making a recovery.
Confirmation of human infections and fatalities in the world's most populous nation has raised the stakes for Chinese and global health authorities in battling the virus.
"That's always of course possible...as long as there are poultry outbreaks, people will be exposed to the virus. You can expect that people might get infected"
WHO's China head
More than 60 people have already died of the H5N1 strain in Southeast Asia since 2003, with most of the deaths in Vietnam, Thailand and Indonesia.
Although human-to-human transmission has not yet been proved, scientists warn that continued contact between infected birds and humans might result in the virus mutating into a form that could be easily passed on between people.
China has the world's biggest poultry industry, with billion of chickens existing in cramped conditions and close to humans, especially in rural areas.
Adding to the danger is that three of the world's major bird migratory routes pass through China. Migratory birds are regarded as the main carriers of the virus around the world.
In an effort to reassure the nation, Premier Wen Jiabao said China would defeat the bird flu just as it overcame the Severe Acute Respiratory Syndrome crisis more than two years ago.
China is stepping up efforts in studying the efficiency of traditional Chinese medicine to help prevent or control human cases of bird flu, Xinhua news agency said.
The State Administration of Traditional Chinese Medicine has launched a working group to supervise and coordinate the study, according to the agency.