The man, asymptomatic, tested positive as he landed in the Hong Kong International Airport on July 18 following a two-week business trip to Los Angeles.
But he first tested negative on July 2 in Hong Kong before bounding for the US.
His latest test result indicated the L452R mutant strain - present in the highly contagious Delta variant first found in India, and a high viral load.
The lockdown was imposed on the 27-story Centre Point on Staunton Street at 7.30 pm, after the man had stayed in the residential complex over the past 21 days.
Residents living there are also required to stay in their premises and undergo testing by 7 am tomorrow.
Those who had been at Centre Point for more than two hours from June 27 to June 19 must also undergo testing by July 21.
However, those hit by the lockdown but had undergone testing from July 17 to 19 and are able to present their test results, can be exempted from another testing.
“However, they are required to stay in their premises until all such persons identified in the area have undergone testing and the test results are mostly ascertained,” the government spokesman said.
Meanwhile, the man’s office in Pacific Plaza on Des Voeux Road West, where he last visited on July 2, has also been added to the compulsory testing list.
Hong Kong recorded zero cases today, with the total tally of infections standing at 11,959 so far - including 212 deaths.
Natural phenomenon, also known as algal blooms, sighted in several coastal areas including Tuen Mun, Tsuen Wan and Tung Chung recently.