Health officials in western China are urgently investigating an unidentified illness which has killed nine farmers and put 11 more in hospital.
The farmers were taken ill with symptoms including high fever and vomiting during June and July.
All the victims, who came from Sichuan province, had recently slaughtered pigs or sheep, local media said.
The researchers are hoping to establish quickly whether the illness is bird flu, which has been found in pigs.
The reports came a day after Indonesia announced the slaughter of 100 pigs near the homes of the first three people in the country to die of bird flu.
Experts have expressed fears that pigs, which can also carry human influenza, could accelerate mutation of the virus into a form which can be transmitted between people.
However, an unnamed official told the Washington Post newspaper that bird flu had been ruled out as a cause of death. No official announcement has yet been made.
Hong Kong fears
Chinese media said the farmers suffered flu-like symptoms during the early stages of the disease but later developed bleeding under the skin and went into shock.
Only one patient has so far recovered, while six of the 10 still in hospital are in a critical condition.
None are thought to have had contact with each other.
The outbreak led Hong Kong health officials to issue a warning to hospitals to look out for similar symptoms.
Correspondents say the territory has been wary of diseases spreading from mainland China since the outbreak of the acute respiratory disease Sars, which killed nearly 300 people there in 2003.