Chinese officials have imposed new limits on movement in some northern parts of the country following a spate of new coronavirus infections, in a sign of how difficult it will be to fully recover from an outbreak that virtually paralyzed the country.

The restrictions imposed over the past week include the city of Harbin, a city of 10 million in northeastern China where a number of new infections have been reported. Other cities in the region have also imposed restrictions, which include preventing outsiders from visiting other neighborhoods and warning residents to stay away from high-risk areas.

The new limits came after the authorities reported dozens of new infections, according to Chinese state media, all of which experts said were linked to the return of Chinese nationals from Russia and the United States. Though the numbers officially disclosed have been modest so far, it is not clear that the spread has been entirely contained.