You can't use the Mainland China Work Permit to work in Hong Kong, you have to apply for Employment Visa of Hong Kong, the following documents are required:
1. An application form ID (E) 936, with relevant parts duly completed and signed;

2. A copy of the sponsor's Business Registration Certificate, Certificate of Incorporation and/or Memorandum of Incorporation and Articles of Association;

3. Financial standing of the sponsor/sponsor's company (income tax return, trading profit and loss account, profit tax return);

4. Company staff list with salary offered and position held and list of expatriate staff previously or currently recruited from overseas;

5. A copy of the applicant's service contract or letter of appointment with details of post, salaries and benefits;

6. Full description of the applicant's post;

7. Details, with proofs, of applicant's academic qualifications and experience relevant to the post, e.g. copies of diplomas, certificates and testimonials;

8. A letter, with supporting proof from the employer (if possible), stating the reason why the post cannot be filled locally;

9. If the applicant is to replace someone already working in Hong Kong, the personal particulars and his whereabouts (if known) should be given;

10. If the applicant is to fill a new post, explain why his/her services are essential;

11. Evidence of the applicant's past residence in Hong Kong (if any);

12. Other information/documents in support of the application required by the concerned officer in individual cases.