Application for registration of designs needs to be made to each country or jurisdiction separately.
Each place will independently decide whether it will register a design in that place.
So, protection for a design registered in the Hong Kong SAR does not extend to the Mainland China, nor elsewhere in the world. Similarly, a design registered in the Mainland China, or elsewhere in the world does not cover the Hong Kong SAR.
You can apply for the registration of a design in each separate country or jurisdiction where you want to seek protection.