You can submit your visa application to Cameroon embassy in Beijing. General processing time is 5-10 working days. The needed requirements are: 1. your passport valid for more than 6 months; 2. 2 passport photos; 3. Invitation letter from Cameroon; 4. Covering letter from your company in China; 5. application form; 6. return ticket 7. Your residence permit valid for next few months in China.