The winter is traditionally the high season for bird flu infections.
In a statement late on Wednesday, the Hong Kong government's Centre for Health Protection said it had informed of the case by mainland China's health ministry, the National Health and Family Planning Commission.
According to the commission, this was the first case of human infection with the H7N4 strain in the world, the Hong Kong government said.
The case involved a 68-year-old woman in Jiangsu province who developed symptoms on Dec. 25, was admitted to hospital on Jan. 1 and discharged on Jan. 22.
"She had contact with live poultry before the onset of symptoms. All her close contacts did not have any symptoms during the medical surveillance period," the Hong Kong government said.
It cited the Chinese Centre for Disease Control and Prevention as saying the virus' genes "were determined to be of avian origin".
The H7N9 strain is far more common in China for humans.