Authorities have locked down two buildings in North Point and Tuen Mun on Tuesday night after preliminary positive cases were identified in the blocks.
In a statement, the government said everyone living in phase three of Maple Gardens on Kin Wah Street, as well as block three of Po Tin Estate on Ming Kum Road have to be tested overnight.
Authorities say the operation in North Point is expected to last until 6:30am, while the one in Tuen Mun will be completed by 7am.