Yes, you are required to apply for a visa in advance through Chinese embassy in Dubai or better send your application to Hk immigration Department directly. Chinese embassy may not accept your application or they need also send it to HK for approval.
The requirements are Visa Application Form, A copy (A-4 size) of the passport and U.A.E. residence visa, An employment/no-objection letter from the company, which clarifies your full name, position, nationality, passport number and the purpose of the visit, and a copy of the trade license, if self-employed, An invitation letter from the sponsor in Hong Kong (for business visit), Detailed schedule, confirmed hotel reservation and round air ticket booking (for tourism) and an original personal bank statement for the last three months.
Generally, it takes 4 weeks for visa processing from HK.