International driving license

You need to apply the International Driving Permit (IDP) in your own country, i.e. Hong Kong.
In the US, you need to have a valid US driving license in order to apply for the IDP. It is clearly stated in the US IDP application form:
Issuance of Permit is restricted to persons EIGHTEEN YEARS or over who hold a valid U.S.A. or Territorial License. PERMIT VALID FOR ONE YEAR. Not renewable.
So, go to the Transport Department and get the IDP.

2008-03-06 16:57:31 補充：
The rationale behind is that only your own country will know the validity of your local license.