You can just apply for a tourist visa with the following documents from the Chinese embassy in Nigeria.
1. Your valid passport with blank pages and at least 6 months validity.
2. A completed application form (ID 1003A which can be download from www.immd.gov.hk) affixed with he applicant's recent photograph.
3.Proof of adequate funds to cover the duration of his/her stay without working.
4. Photocopy of the applicant's travel document containing personal particulars, date of issue, date of expiry and/or details of any re-entry visa held (if applicable)
5.Photocopy of proof of transportation arrangement, e.g. flight itinerary
6. Photocopy of proof of the proposed visit to Hong Kong.
4.