Genome sequencing showed a 62-year-old man and a 50-year-old woman – who arrived from the UK on Friday and were listed as confirmed cases on Sunday – were carrying the Omicron variant.
Both of them were fully vaccinated and tested positive for the virus at the Hong Kong International Airport.
The Centre for Health Protection said there has not been any spread of the Omicron variant in the community, as all seven cases were detected within the restricted area at the airport or at designated quarantine hotels.
It added that authorities would adopt the most stringent prevention and control measures to prevent the mutant strain from entering the community.
Meanwhile, there were two new imported Covid-19 cases on Monday.
They included a 75-year-old man who flew in from Pakistan and a 50-year-old man who had been to Tanzania, South Africa and Kenya.
Both of them tested positive for the virus during quarantine.