The Centre for Health Protection said the patients, who arrived from Switzerland, Russia and the Philippines, carried the L452R variant and have all been fully vaccinated.
All of the cases reported in Hong Kong in the past two weeks were imported.
Health authorities added there were fewer than five preliminary positive infections.
Meanwhile, officials are following up on two positive cases involving people travelling from Hong Kong to the United Kingdom.
One of them is a 16-year-old boy who lived in Block 19 of Baguio Villa at Pok Fu Lam and left for the UK on August 26.
The teenager, who was fully vaccinated, had tested negative before he left Hong Kong, but his specimen collected in the UK on September 6 came back positive.
The other patient is a fully-vaccinated 51-year-old man who lived in Block 3 of Kent Court on Boundary Street and left Hong Kong on September 1.
His test on August 30 came back negative, but the man developed symptoms and tested positive after arriving in the UK.
Officials said residents of the buildings where the pair lived during the incubation period will have to undergo compulsory Covid testing.