The son and daughter of a Saudi Arabia consul tested preliminarily positive for a more infectious Covid-19 mutant strain, triggering an overnight lockdown at Tang Kung Mansion in Taikoo Shing.
Leon Court in Wan Chai was another block that went into lockdown last night, making it the second night in a row for mandatory testing after a resident returning from France was found to carry the mutant strain.
The Taikoo Shing cases involved a 13-year-old and her 11-year-old brother who arrived from Saudi Arabia on Friday. As the children of a consul, sources said, they were allowed to observe quarantine at home.
The girl tested positive for the L452R mutant strain - commonly found in the Delta variant - while test results are awaited for the boy.
Despite testing negative at the airport, their saliva samples submitted on the third day of their arrival came back as preliminarily positive.
The Wan Chai lockdown was triggered by a man, 39, who left for France on July 2 and returned on Sunday through Doha. He tested positive for the L452R strain on arrival.
He had completed both doses of the BioNTech/Fosun jabs in April.
Although authorities believe the man and the two children were likely infected in France and Saudi Arabia, they cordoned off the blocks at 7.30pm and 8pm to test all residents as a precaution.
On Monday night, Centre Point in Sheung Wan was locked down after a 27-year-old male tested positive upon returning from the United States.
This came as Hong Kong yesterday recorded seven imported cases from the United States, Japan, France, Iran and Bangladesh, taking its tally to 11,966, including 212 deaths.
A Qatar Airways flight, QR 818 from Doha, carried four passengers confirmed with Covid-19 upon landing on July 18, prompting authorities to ban flights from Doha operated by the airline until August 2.
Also, authorities have further delayed start of the air travel bubble due to a surge of cases in Singapore and will review the policy next month.
Meanwhile, an epidemiologist suggested that "learning to live" with the coronavirus would be a more sustainable strategy for Hong Kong after Britain on Monday lifted pandemic restrictions after 17 months.
The University of Hong Kong's Benjamin Cowling said Hong Kong can take Britain's approach as a reference.
"I think if we can get a high vaccination coverage, then learning to live with the virus, like they're doing in the UK, might be a better, longer-term strategy," he said. "We'll have to do that sooner or later anyway."