A medical worker collects a swab sample from a child at a community in Yuhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. (Xinhua/Jin Haoyuan)

A medical worker collects a swab sample from a resident at a community in Yuhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. (Xinhua/Jin Haoyuan)

Medical workers seal a sample at a community in Yuhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. (Xinhua/Jin Haoyuan)

A medical worker works at a community COVID-19 testing site in Xinhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. The city has set up 5,011 sites to collect swab samples for the tests. (Xinhua/Yang Shiyao)

Medical workers put their hands together to encourage each other before conducting COVID-19 tests at a community in Yuhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. The city has set up 5,011 sites to collect swab samples for the tests. (Xinhua/Yang Shiyao)

A police officer stands guard at an entrance to the expressway in Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. The city has set up 5,011 sites to collect swab samples for the tests. (Xinhua/Yang Shiyao)