Just finished watching SHI MIAN (The Sleeping Curse), a Herman Yau directed and Anthony Chau-Sau Wong starring movie.
After doing some research and reading that this would be their last horror collaboration, I found out of two other movies that they did before: Bat sin fan dim: Yan yuk cha siu bau (THE UNTOLD STORY) and Yi boh lai beng duk (THE EBOLA SYNDROME). I'm now trying to find a subtitled copy, but read that these movies are categorised as Category III films.

Is Category III a rating system overall or just for horror movies, and if the latter, what other HK horror movies are there that meet this criteria?
Is there also a higher category?

Category III is one rating in a classification system that also has Category IIB, IIA, II, and I. And these categories are for all movies. Me and stuffp recently saw a Category III at the cinema (Fifty Shades Freed). Cat III is the HK equivalent of an R/NC-17 in the US (or 18 in the UK), and it is the highest category there is.

Many thanks.

That's what I thought, but one article made it look like it could be a horror specific rating.

Great detailed explanation.

Glad to help.

This has made me think of a few other Cat III films I've seen in Hong Kong now. I saw a brilliant sex comedy called Due West: My 3D Sex Journey (also referred to as other names but back in 2013 that was the English title), and also Logan, if I remember correctly, was Cat III. I haven't seen all that many. Maybe five or six. It's a good feeling the first few times. Feels like you're seeing something taboo, but honestly it's just tits/ass or excessive gore, not porn or snuff level. But I do prefer a ratings system over no ratings system (like in China).