As far as I know China/Hong Kong is part of the so called "Madrid Agreement". If your trademark is succesfully registered on a national level, you can register it in x-number of member countries via the World Intellectual Property Organisation (WIPO) in Geneva. Depending on the number of countries you select and how smooth the process is, it can easily cost you up to EUR 10,000 (this number is based on a registration which included a number of member countries in Western and Eastern Europe as well as Japan & China).
For the US, as well as other non-member countries (eg in South East Asia), we were told that you will have to register on a national level, which can be very time consuming and cost you another substantial amount.
I am no lawyer and was not directly invovled in the registration process my company went through, so better treat this info carefully.
You can try to read up here:
www.wipo.int/madrid/en/
(I saw they even have a fee calculator)