China's port city Dalian has extended quarantine to 21 days for people who may have been exposed to the new coronavirus from 14 days previously, as it battles a rise in new infections and observes a long virus incubation period.

The city in the northeastern Liaoning province has reported a total of 50 confirmed Covid-19 patients since a recent outbreak started around mid-December, the city government said, according to Reuters.

“Because of the long incubation period and rapid transmission speed [...] some cases didn't show positive result until 11 times of nucleic acid tests,” Tang Yi, head of the Dalian civil affair bureau, said at a news briefing.

Tang said maintaining a 14-day home quarantine could bring some danger to epidemic control, as situations have become more complex.