Hong Kong has confirmed its first case of the new strain of the H7N9 bird flu in a domestic worker from Indonesia.
The worker, 36, recently travelled to Shenzhen in the mainland and came into contact with live poultry. She is in critical condition, officials say.
H7N9 has infected more than 100 people since it emerged earlier this year.
The case in Hong Kong is a sign that the virus may be spreading beyond mainland China, where most infections have been reported, and Taiwan.
The World Health Organization (WHO) had said there was "no evidence of sustained human-to-human transmission", but also described H7N9 as an "unusually dangerous virus".
At least 139 human cases of H7N9 have been confirmed, including 45 deaths, WHO says in a statement dated 6 November.
At least one case was confirmed in Taiwan in April.
Dr Ko Wing-man, Hong Kong's food and health secretary, confirmed the territory's first H7N9 case late on Monday.
He said that the patient "has a history of travelling to Shenzhen, buying a chicken, slaughtering and eating the chicken".
"She is now in critical condition at Queen Mary Hospital," he said, adding that four people in close contact with her were showing signs of flu-like symptoms.
Hong Kong is now on public health alert and has suspended the import of live chickens from some farms across the border with the mainland.
H7N9 is a type of influenza virus that normally circulates among birds and has not until recently been seen in people, the WHO says.
"There is no indication thus far that it can be transmitted between people, but both animal-to-human and human-to-human routes of transmission are being actively investigated," the organisation adds.