Health officials said the patient, 27, lives in Wan Hang House on Wan Tau Tong Estate and has had no recent travel history.
He came into contact with cargo flight crews, and he last went to work at the airport last Wednesday.
The man also worked part-time at customer service at Tai Po’s Uptown Plaza, and last worked there on Tuesday.
The day before, he developed symptoms including fever, sore throat and cough, and a deep throat saliva sample tested preliminarily positive and carried the L452R strain.
Wan Hang House was put on lockdown on Wednesday evening, with residents required to undergo compulsory Covid testing.
The government hopes to end the operation by 7:30am on Thursday.
The news came after residents of more than 30 Tai Po buildings were ordered to test for Covid-19, after a very high viral load was detected in sewage samples in the district.
Anyone who’s been in the area for more than two hours in the past two weeks is required to get tested by Friday.
People who are fully vaccinated are exempt.
A specialist in respiratory medicine, Leung Chi-chiu, said he’s concerned this could be the start of a fifth wave of local infections.
“It’s a serious warning sign… not only was there a high viral load, it’s also the extent of the spread within that area,” he told RTHK.
“If it involves so many buildings within such a short period of time, it means the virus has very high efficiency in transmission, and quite a number of people would have been infected.”