Residents line up to take COVID-19 nucleic acid tests in Macao, south China, Aug. 4, 2021. The mass testing, started from 9:00 a.m. local time Wednesday, is expected to be completed within three days, according to the Novel Coronavirus Response and Coordination Center of Macao. (Photos: Xinhua/Cheong Kam Ka)

Medical workers take swab samples from residents for COVID-19 nucleic acid testing in Macao, south China, Aug. 4, 2021. The mass testing, started from 9:00 a.m. local time Wednesday, is expected to be completed within three days, according to the Novel Coronavirus Response and Coordination Center of Macao.

Residents wait to take COVID-19 nucleic acid tests in Macao, south China, Aug. 4, 2021. The mass testing, started from 9:00 a.m. local time Wednesday, is expected to be completed within three days, according to the Novel Coronavirus Response and Coordination Center of Macao.

A medical worker takes a swab sample from a resident for COVID-19 nucleic acid testing in Macao, south China, Aug. 4, 2021. The mass testing, started from 9:00 a.m. local time Wednesday, is expected to be completed within three days, according to the Novel Coronavirus Response and Coordination Center of Macao.

A medical worker takes a swab sample from a resident for COVID-19 nucleic acid testing in Macao, south China, Aug. 4, 2021. The mass testing, started from 9:00 a.m. local time Wednesday, is expected to be completed within three days, according to the Novel Coronavirus Response and Coordination Center of Macao.