A teenager from China's eastern Anhui province has become the country's 15th victim of the bird flu virus, the health ministry officials have said.
The death of a 16-year-old boy on Tuesday night - almost two weeks after developing symptoms of the H5N1 virus - has raised concerns over the country's monitoring standards.
"This is the 23rd out of 24 human outbreaks in China where we weren't forewarned by a poultry outbreak," Joanna Brent, the World Health Organisation spokeswoman in Beijing, told the AFP news agency.
Health officials said the boy had no history of contact with dead or sick birds, while no outbreaks of the virus among animals had been reported in the province.
In most cases elsewhere around the world, the disease has been traced to either an outbreak amongst animals or contact between the victim and dead or sick animals, Brent said.
In the light of the latest case she urged Chinese officials to strengthen monitoring and surveillance of bird flu among animals.
"This is not consistent with what we are seeing around the world," she said.
Of the 24 patients confirmed with bird flu infections in China since 2003, 15 have died.
The last human death was of a 44-year-old woman in eastern China reported in February.
Scientists say that multiple strains of the disease originated in southern China and spread elsewhere.
Rising toll
The boy's death brings to 170 the number of people who have died from bird flu around the world, but does not include the latest deaths in Indonesia.
On Thursday, Indonesia announced two more deaths from the bird flu virus, taking its human toll to 69, the highest in the world.
Runizar Ruesin, a health ministry official, said one person died on Sumatra island while the other in an army hospital in the capital Jakarta.
"They tested positive in the first test," he said, adding a second was being conducted to confirm initial results.
Most human cases in Indonesia have occurred after contact with sick birds, prompting a ban on keeping backyard chickens in Jakarta in the hope of eradicating human infections this year.