The global financial hub has fewer Covid-19 curbs than the rest of China, but it still does not treat the virus as endemic, as most of the world does. That dissuades tourists and many business travellers from entering.
In a statement on Monday, the Hong Kong government said Lee would undergo quarantine after testing positive in a PCR test at the airport the previous night.
"During the isolation period, John Lee will work from home and attend meetings via video as needed," it said, adding that rapid antigen tests Lee took on each day of his four-day trip had all proved negative.
Asked about Lee testing positive after meeting Xi in Bangkok, Chinese foreign ministry spokeswoman Mao Ning said the "Chinese delegation has made appropriate arrangements according to Covid-19 prevention rules."
Hong Kong tests all arrivals at its airport, with those testing positive required to isolate, while those who are negative must avoid bars and other venues for three days.
(Reporting by Twinnie Siu; Editing by Anne Marie Roantree, Clarence Fernandez and Toby Chopra)

Hong Kong Chief Executive John Lee attends the APEC Leaders' Informal Dialogue with Guests during the Asia-Pacific Economic Cooperation (APEC) Summit 2022, in Bangkok, Thailand, 18 November 2022. EPA-EFE/ATHIT PERAWONGMETHA / POOL