[Apologies / let me know if this is off-topic for B Movie Bonanza]
Two-part article from Eastern Kicks
- The Gory Glory Days of Hong Kong Category III Cinema – part 1 (some gory images)
- The Gory Glory Days of Hong Kong Category III Cinema – part 2 (some NSFW or gory images)
TL,DR:
Despite being one of the world's centres of film production back then, laissez-faire colonial Hong Kong didn't have any system of film classification or censorship until a film came out in 1988 (Men Behind the Sun) that was so egregious, it almost single-handedly created the political impetus to introduce a film classification law and system.
The most restricted classification was Category III, which made it a crime for anyone under 18 to watch.
Rather than shut down the worst productions, it unleashed a boom as many producers treated Cat III status as both a licence and a badge of honour, indulging in the greatest excesses in exploitation cinema: soft-core porn, torture, rape and cannibalism. And, to be frank, a lot of misogyny :(
And unlike an X rating or NC-17 classification in other countries, Cat III certification wasn't the kiss of death for mainstream respect and business, with Cat III films shown in mainstream cinemas, actors appearing in both mainstream and Cat III films, and some Cat III films even winning mainstream awards. (Actors like Anthony Wong, Simon Yam and Shu Qi got their start and first critical acclaim in Cat III exploitation.)
The boom faded as the 90s ended, as the novelty wore off and Hong Kong came under PRC control, but there are still some occasional Cat III films made, often in the sex comedy genre.
Personally, while I watched a lot of HK movies in the 90s, I wasn't into Cat III (although I would curiously read about their excesses in mags like Impact or zines like Trash City [some images NSFW or gory]).
I got thinking about Cat III again when watching (the absolutely not Cat III) Future Cops (from @[email protected] 's post). I chuckled when at the end Chun-May almost kisses Ti-Man but is too chaste to go through with it, given that the actress Chingmy Yau was largely famous for doing Cat III softcore porn / "girls with guns" exploitation flicks like Raped by an Angel (1992) and Naked Killer (1993), by the very same director as Future Cops, Wong Jing.
Category III film links
Links may lead to NSFW or gory images
Eastern Kicks has a category ;) called Category III to see some reviews of Cat III films.
City on Fire search for "category III"
City on Fire review of the "original" Cat III film, Men Behind the Sun
Men Behind the Sun comes with the reputation of being one of the most controversial movies ever made, often mentioned in the same sentence as the likes of Ruggero Deodato’s Cannibal Holocaust, and Japan’s Guinea Pig series. The facts certainly indicate the same – it holds the distinction of being the first movie to be rated Category III in Hong Kong, has been released in very few territories uncut, was originally banned in Australia, and caused such an outcry in Japan that the director received death threats.

Not into rape? The movie you used for the image is called Raped by an Angel, also known as Naked Killer 2
The poster is emblematic of that whole phase of HK cinema, doesn't mean I actually want to watch rapes being depicted.
So, yes, I am not into rape.