China reported two human cases of bird flu in the southwestern city of Guiyang on Sunday, with both patients in a critical condition, the official Xinhua news agency said.

A 21-year-old woman and 31-year-old man tested positive for the H5N1 bird flu virus on Sunday after developing symptoms on February 2 and February 3 respectively, Xinhua said.

"They are in a critical condition and medical workers are carrying out emergency treatment," the Ministry of Health said in a statement, cited by Xinhua.

People who had close contact with the two patients are under medical observation but none have been found ill so far, the agency said. It reported that the pair did not have contact with birds before they developed symptoms.

The bird flu virus has killed 365 people worldwide since a major outbreak in 2003, according to the World Health Organisation.

It typically spreads from birds to humans through direct contact, but experts fear it could mutate into a form transmissible between humans.

China is considered one of the nations most at risk from bird flu epidemics because it has the world's biggest poultry population and many chickens in rural areas are kept close to humans.

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(c) 2013 AFP