A 41-year-old man in China's eastern province of Jiangsu has been confirmed as the first human case of infection with a rare strain of bird flu known as H10N3, China's National Health Commission has said.
Many different strains of bird flu are present in China and some sporadically infect people, usually those working with poultry.
There is no indication that H10N3 can spread easily in humans.
The man, a resident of the city of Zhenjiang, was hospitalised on 28 April and diagnosed with H10N3 on 28 May, the health commission said.
It did not give details on how the man was infected.
He is now stable and ready to be discharged.
Investigation of his close contacts found no other cases, the NHC said.
No other cases of human infection with H10N3 have been reported globally, it said.
H10N3 is low pathogenic, which means it causes relatively less severe disease in poultry and is unlikely to cause a large-scale outbreak, the NHC added.
The strain is "not a very common virus," said Filip Claes, regional laboratory coordinator of the Food and Agriculture Organization's Emergency Centre for Transboundary Animal Diseases at the regional office for Asia and the Pacific.
Only around 160 isolates of the virus were reported in the 40 years to 2018, mostly in wild birds or waterfowl in Asia and some limited parts of North America, and none had been detected in chickens so far, he added.
Analysing the genetic data of the virus will be necessary to determine whether it resembles older viruses or if it is a novel mix of different viruses, Mr Claes said.
There have been no significant numbers of human infections with bird flu since the H7N9 strain killed around 300 people during 2016-2017.