A child reacts while undergoing nucleic acid testing in Wuhan, the Chinese city hit hardest by the coronavirus disease (COVID-19) outbreak, Hubei province, China May 16, 2020. As Wuhan, the Chinese city where the COVID-19 pandemic began, revs up a massive testing campaign, some residents crowding the test centres expressed concern on Saturday. REUTERS/Aly Song

A woman wearing a face mask looks on in front of others standing in a queue for nucleic acid testings in Wuhan, the Chinese city hit hardest by the coronavirus disease (COVID-19) outbreak, Hubei province, China May 16, 2020. The new cases - all of them people who had previously shown no symptoms of the disease - spurred Wuhan authorities to launch a citywide search for asymptomatic carriers of the virus. REUTERS/Aly Song

Residents wearing face masks line up for nucleic acid testings in Wuhan, the Chinese city hit hardest by the coronavirus disease (COVID-19) outbreak, Hubei province, China May 16, 2020. he unprecedented scale of testing indicates the official level of concern, some experts say. Others say it is an extremely costly exercise and question its effectiveness. REUTERS/Aly Song

A child reacts while undergoing nucleic acid testing in Wuhan, the Chinese city hit hardest by the coronavirus disease (COVID-19) outbreak, Hubei province, China May 16, 2020. Many people observed social distancing, such as queuing 1 metre apart, and there were signs to remind them. REUTERS/Aly Song

Residents wearing face masks queue for nucleic acid testings in Wuhan, the Chinese city hit hardest by the coronavirus disease (COVID-19) outbreak, Hubei province, China May 16, 2020. REUTERS/Aly Song

Residents line up for nucleic acid testings at a residential compound in Wuhan, the Chinese city hit hardest by the coronavirus disease (COVID-19) outbreak, Hubei province, China May 15, 2020. REUTERS/Aly Song