Two of the patients carry the more contagious L452R strain, officials said, while the result of the third patient was pending.
The Centre for Health Protection said residents of Tang Kung Mansion in Taikoo Shing and Leon Court in Wan Chai have to undergo compulsory testings and remain at their flats until the operations end at about 7am on Wednesday.
Officials said the lockdown in the Taikoo Shing block had to do with a 13-year-old girl and her 11-year-old brother who arrived from Saudi Arabia last Friday and “underwent self-isolation at home upon arrival according to relevant arrangement of exempted persons.”
Their Covid tests at the airport were negative, but the deep throat saliva samples submitted on day three after their arrival came back preliminary positive.
The girl developed fever on July 17 and was found to carry the L452R strain, while the boy was asymptomatic.
It’s understood they are the children of a Saudi official in Hong Kong.
The Wan Chai case, meanwhile, relates to a 39-year-old man who travelled to France on July 2 and returned on Sunday. He tested positive for Covid-19 upon arrival here and was found to carry the L452R strain.
He had lived in Leon Court before leaving for France.
“The patient has lived in Wan Chai within the past 21 days, the risk of infection in the relevant area is assessed to be likely higher,” a government spokesman said.
The authorities believe all three patients were infected overseas because they spent the majority of their incubation period outside Hong Kong, and the cases were classified as imported.