Dead chickens were found on a farm in Anhui province on Saturday, and tests have since confirmed that they died of bird flu, the government said on state-run television.
Since the farm is in an isolated area and the birds were hatched locally, agriculture experts believe the disease was brought to the area by migrating birds, the report said.
Bird flu has also reemerged on farms in Thailand and Vietnam in recent days.
World health experts fear that a strain of bird flu could lead to a pandemic in humans, but China has reported no cases of humans catching the disease from poultry.
At its height earlier this year, bird flu ravaged flocks throughout Asia. It spread to humans in Vietnam and Thailand, killing 24 people. About 100 million chickens across the region were slaughtered to halt its spread.
China declared it had "stamped out" the disease in March after slaughtering 9 million chickens and other poultry. But it warned that the disease might come back with warmer weather.
"It's not surprising that it has come back," said Roy Wadia, a spokesman for the World Health Organization in Beijing. "It stays in the environment a long time."
The farm, in the city of Chaohu near a scenic lake with the same name, has been quarantined, China Central Television said.
Authorities killed all the poultry within two miles of the affected farm and vaccinated poultry within three miles, in line with established control measures, the report said.
It added that the outbreak was under control.
According to Wadia, "I think the experience that China had several months ago has prepared it well."
He said the U.N. agency was monitoring China's outbreak as well as other cases in Asia.
In Thailand on Tuesday, the government announced a suspected outbreak at a farm in a central province. In Vietnam, new outbreaks have been reported in the Mekong Delta.
By Stephanie Hoo