Experts have traveled to the infected region in Yushu County, about 800 km from the provincial capital Xining, and medical measures have been tightened to halt the spread of the virus, said Mao Qun'an.

However, he warned against complacency as the possibility of a large-scale outbreak cannot be ruled out.

The Ministry of Agriculture confirmed on May 5 that wild birds found dead in Yushu were infected with the H5N1 strain of bird flu.

The virus killed thousands of migratory waterfowls in the Qinghai Lake a year ago and the World Health Organization (WHO) says the form of the H5N1 virus is almost identical to the strain found in recent outbreaks in Nigeria, Iraq and Turkey.

The Chinese Ministry of Health issued a notice last week, requiring all local health authorities to report any human cases of unknown pneumonia and anatomize dead bodies.

In China, 12 people are known to have died of bird flu and six have survived. Worldwide, 115 people have died in nine countries.

The virus remains a disease in birds and is hard for humans to catch, but health experts worry that the virus could mutate into a form that easily transmits among humans.