Chinese authorities are testing millions of people, imposing lockdowns and shutting down schools after multiple locally transmitted coronavirus cases were discovered in three cities across the country last week.

As temperatures drop, large-scale measures are being enacted in Tianjin, Shanghai and Manzhouli, despite the low number of new cases compared to the US and other countries that are seeing new waves of infections.

Many experts and government officials have warned that the chance of the virus spreading will be greater during the cold weather. Recent flare-ups have shown that there is still a risk of the virus returning, despite being largely controlled within China.

On Monday, the National Health Commission reported two new locally transmitted cases in Shanghai over the last 24 hours, bringing the total to seven since Friday.

China has recorded 86,442 total cases and 4,634 deaths since the virus was first detected in Wuhan late last year.

The two latest cases confirmed in Shanghai were close contacts of another airport worker who was diagnosed with Covid-19 earlier in November. On Sunday night, the city’s Pudong International airport decided to test its workers, collecting 17,719 samples till the early hours of Monday morning