China could suffer a "massive" outbreak of bird flu this spring, the Chinese agriculture minister has said.
China has been put on its guard by warnings from officials
The minister, Du Qinglin, was speaking to parliamentarians after China reported two new human cases of the potentially lethal H5N1 strain.
Officials are worried that wild birds will infect farm poultry as they return from their winter migration.
"We must remain on a high-level alert in all areas ... and step up prevention and control work," the minister said.
"The possibility of a massive bird flu outbreak cannot be ruled out," Mr Du said in a briefing to MPs.
In 2005, China was hit by more than 30 outbreaks of bird flu.
In their efforts to bring the epidemic under control, authorities have slaughtered more than 23 million birds and embarked on a massive vaccination drive.
Two new cases
The two new human cases of the disease were identified as a nine-year-old girl in eastern Zhejiang province and a woman farmer in neighbouring Anhui province, Xinhua news agency said.
Both are listed as being in critical condition.
The woman farmer, who had come down with the virus on 11 February, had been in contact with sick and dead poultry, the agency said.
The girl was said to have visited relatives who kept poultry.
"During her visits, chickens raised at her relatives' homes got sick and some died," Xinhua said.
Fourteen people have caught the virus in China this winter, of whom eight have died.
H5N1 has killed more than 90 people, mostly in Asia, since late 2003.
It can be caught by humans who handle infected birds, but is not yet known to have passed from one person to another.
Scientists have warned that if the virus mutates, it could create a pandemic that could kill millions of people.