Added surveillance bonus(!) at Mainland Chinese airports: When doing international to international transfers, you are required to have your passport scanned. I have never seen this in free countries. You just wait in an international terminal (no customs, etc) and take the next flight. I am curious if CCP will require HK Airport to change their rules/procedures in the future.

In Singapore Changi, the arrival and departure are at same gate so you can just sit and wait for next flight. Passport is checked before you get into next flight at the gate where they check your boarding pass as well..right there your bags are also scanned (at each gate or group of few gates)

Just transited in HKG, the gates are same but boarding at different levels. So you clear the security at a common area, get same PP checks done then go to departure gate which is one level above. IIRC Qatar etc are the same.

But PP checks do happen in both cases.