In Hong Kong, just like in the UK, English common law applies. So unlike Mainland China, prostitution itself is perfectly legal here as long as it’s not conducted inside a brothel *Used wholly or mainly by 2 or more persons
“One-woman brothel” buildings have existed since Colonial times & are scattered about the centre of the city. Each building has tiny micro-apartments with just a bedroom & bathroom. Because it’s a private home with only one woman working alone, it’s not classified as a brothel even though a 100 to 200 or so working women reside in the building.