A worker in a protective suit guards the entrance to a historic building in Shanghai on March 28. China has tightened restrictions to battle a resurgence of Covid-19. On Tuesday, the country reported more than 20,000 new locally transmitted cases. Photo: VCG

Workers spray disinfectant Tuesday inside a locked-down residential community in Shanghai, which reported 17,077 new local cases that day. Photo: Aly Song /IC Photo

Covid-19 control personnel prepare nucleic acid tests for residents in a residential complex in the city of Jilin in the northeastern province of the same name. Photo: VCG

A volunteer helps a resident register for a nucleic acid test Tuesday at a residential community in Jilin’s capital of Changchun. The province reported 2,735 new local cases that day. Photo: VCG

A volunteer goes door to door in a residential community Thursday to register residents for mass testing in Suining, Southwest China’s Sichuan province. Sichuan confirmed 10 new cases of Covid-19 on Tuesday. Photo: VCG

Volunteers deliver vegetables Thursday to residents under lockdown in Ningbo, East China’s Zhejiang province. Zhejiang reported 67 new local cases on Tuesday. Photo: VCG

A disease control worker checks vehicles Sunday at a highway on-ramp in Yuncheng, North China’s Shanxi province. Shanxi reported 10 new local cases Tuesday. Photo: VCG

Wangjing Soho, an office complex in Beijing, was locked down for health monitoring after a case was detected in the area Tuesday, when the city reported five new local cases. Photo: VCG

A street in Sanya, South China’s Hainan province, appears empty Monday after the city implemented Covid control measures. On Tuesday, the province reported 32 new local cases, of which 31 were detected in Sanya. Photo: VCG

Few pedestrians walk the streets on March 30 in Harbin, Northeast China’s Heilongjiang province. Heilongjiang reported 11 new local cases Tuesday. Photo: VCG

Residents stand in line to be tested for Covid-19 on Sunday at a residential community in Quanzhou, South China’s Fujian province. Fujian reported 29 new local cases Tuesday. Photo: VCG