Health authorities said on Thursday one person has tested preliminary positive during an overnight lockdown of a public housing block in Kwai Chung.
Authorities said arrangements were made for the preliminary case to be sent to hospital and the close contact to the quarantine centre.
More than 2,500 people were tested in the operation at Yat Kwai House in Kwai Chung Estate.
Health authorities earlier reported two confirmed or preliminary infections among residents of the building, involving a man, 79, and an air freight worker.