A medical worker takes a swab sample from a citizen for a nucleic acid test in Chengxi District of Xining, northwest China's Qinghai Province, May 7, 2022. (Xinhua/Zhang Long)

Aerial photo shows people lining up for nucleic acid tests in Chengxi District of Xining, northwest China's Qinghai Province, May 7, 2022. (Xinhua/Zhang Long)

A citizen registers for a nucleic acid test in Chengxi District of Xining, northwest China's Qinghai Province, May 7, 2022. (Xinhua/Xie Tongqiang)