Chinese authorities have reported 139 new cases of a mysterious virus in two days, marking the first time that the infection has been confirmed in the country outside of Wuhan city.

The new cases were identified in the cities of Wuhan, Beijing and Shenzhen.

Authorities in the central Chinese city of Wuhan said 136 new cases had been confirmed over the weekend, and a third person there died from the virus.

In total, the city alone has confirmed almost 200 cases of the coronavirus. As of late Sunday, officials said 170 people in Wuhan were still being treated in hospital, including nine in critical condition.

China's National Health Commission on Sunday said the virus was "still preventable and controllable", while warning that close monitoring was needed given that the source, transmission and mutation methods were unknown.