Cantonese is mostly mostly dominant and safe in Hong Kong. It is the language of Guangdong Province (Canton) however, it's being slowly phased out by government efforts [1][2] and by demographics (it's where all the factories are – it attracts Mandarin speakers from rest of China who go there to work and, recent trend, they're starting to settle there).

[1] http://www.businessinsider.com/china-is-forcing-its-biggest-...

[2] https://blogs.wsj.com/chinarealtime/2010/07/26/clash-over-ma...