You need both a visa to Hk and to Beijing.
For the visa to Hk, you need the following documents:
A. Your valid passport with at least 6 months validity and two blank pages left.
B. Properly completed visa application form with one recent passport-size color photograph. Please note incomplete application is not acceptable.
C. Copy of the passport face page.
D. Travel itinerary.
E. Copy of onward visa (the destination visa).
F. Local company covering letter.
G. Company bank statement (latest month).
H. Company pay sheet (last 3 month).
For the visa to Beijing, the requirements are as follows:
A. One truly-filled completed visa application form;
B. One recent passport sized photo;
C. A valid original passport with at least 2 blank pages and 6 months validity left.
D. A valid visa for the country of final destination in addition to an invitation letter or onward airline ticket.