The government on Tuesday locked down a building in Tuen Mun and three blocks in Cheung Sha Wan, after sewage samples in the buildings were found to contain the coronavirus.
People living in Yee Hong House, Yee Yan House and Yee Sau House of Yee Kok Court, as well as Hei Tin House of Yan Tin Estate, are required to get tested overnight.
The operations are expected to finish on Wednesday afternoon.