Police had sealed off the building on Staunton Street on Monday evening after a 27-year-old man, who had arrived back from the US on Sunday, tested preliminary positive for the L452R mutation.
The mutation is present in the very infectious delta variant, but is not unique to it.
The man had lived in the block for about a week, before going on a trip to the US on July 4.
He had been fully vaccinated with the BioNTech vaccine and did not have any symptoms.
Authorities are classifying the case as an imported one, as he may have been infected in America.
Earlier on Monday, health authorities here reported no new Covid-19 infections.
Last updated: 2021-07-20 HKT 08:30