A woman who lives there had tested preliminary positive for the coronavirus.
The 66-year-old had dined with eight relatives at the Moon Palace restaurant in Kowloon Tong on December 27, and would be the sixth Covid patient linked to the cluster there if her infection is confirmed.
Officials moved in to the site at 7pm, and as of 1 am had tested 660 residents in tower two of Granville Garden.
There was no answer at 20 of the units, and officials have said they will follow up.
The government said the operation was completed by 7 am and residents who could prove they had tested negative were allowed to leave.