http://www.immd.gov.hk/ehtml/id1004.htm#III7c
Holders of foreign passports who are living in the Mainland of China may submit the application forms together with all supporting documents to the Immigration Division of the Office of the Government of the HKSAR in Beijing (Beijing Office). Applicants are required to produce their travel documents to the Immigration Division of the Beijing Office so that a visa/entry permit could be issued if the application is approved. The address of the Beijing Office is:
No. 71, Di'anmen Xidajie, Xicheng District
Beijing 100009
People's Republic of China