@AlexA. Geographically, Hong Kong is in Guangdong province. People in Guangdong province largely speak Cantonese, and so most Hong Kongers speak Cantonese. However, there's a really interesting quirk to this. On the Chinese border right on the other side of Hong Kong, is a city called Shenzhen, and because it's a major tech centre with lots of immigrants from other parts of China, Shenzhen is composed mostly of Mandarin speakers.