A woman in southwestern China has died from bird flu, bringing the country's human death toll from the disease to seven, the official Xinhua News Agency said Wednesday.

Xinhua cited the Ministry of Health as saying it was still investigating where the woman, surnamed Cao, contracted the disease. It did not say when she died or give her full name.

The news agency reported Monday that the woman showed symptoms for a fever and pneumonia on Jan. 12 and was hospitalized in a critical condition in Chengdu in Sichuan province.

She tested positive for the H5N1 strain of bird flu on Jan. 17, Xinhua said.

The earlier Xinhua report said that people who have had close contact with Cao have been put under medical observation by local health authorities, but have not shown any abnormal symptoms.

Bird flu has killed at least 79 people in Asia and Turkey since 2003.

Most human infections have been traced to contact with sick birds and Chinese health officials say more are inevitable if the country does not curb outbreaks in poultry.

Experts worry that the virus could mutate into a form that would be easily transmitted between people, sparking a global flu pandemic that could kill millions.