Well, it's a Great Tit, but then things get a little confusing if trying to explain further. The Great Tit is Parus major and had a range covering basically all of Europe and most of Asia, but this has now been split up into several species. The subspecies in Hong Kong is commixtus, which some authors place under the Japanese Tit Parus minor and some under the Cinereous Tit Parus cinereus. I believe the official Hong Kong checklists use P. cinereus.
On my own bird lists I just keep all the Great Tits under Parus major because it is easier that way!
