I am a Sri Lankan citizen working in Africa and now on Holiday in colombo? how do i get china visa?

Need to visit a factory in WUXI (Shanghai) - Company in China is ready to provide invitation letter? Is it better to apply for business F or tourist L in Sri Lanka? What are the documents needed from my side? My company in Africa can provide me documents for VISA but would that be valid in Sri Lanka?
Pls guide me or please let me have an agent in Colombo who can do the needful for me please.