They are among 2,000 residents of Heng Fung House at Heng On Estate who were ordered to get tested on early Tuesday afternoon.
There were also around 15 indeterminate cases.
The building was sealed off after some of its residents tested preliminary positive for the virus. Sewage samples taken from the block also came back positive.
Earlier, a separate lockdown of a block in neighbouring Chung On Estate also picked up 49 preliminary positive cases.