Recently I read an article on traders from the Congo (DRC) in China (PRC), which came as a surprise, as it referred to a few thousand.

According to a Wiki piece there are:
According to a local newspaper report in 2008, the number of Africans in Guangzhou had been increasing by 30-40% each year, and formed the largest black community in Asia....from Nigeria, Mali, Guinea, Cameroon, Liberia nd the DRC....

Academics have attempted to estimate the size of the population. Huang Shiding of the Guangzhou Institute of Social Sciences in 2007 estimated the number of permanent residents of foreign nationality (six months and above) to be around 50,000, of which some 20,000 are of African origin. Roberto Castillo, a graduate student researching Africans in Guangzhou, estimated in 2013 fewer than 10,000 Africans residing in Guangzhou and 20-30,000 Africans travelling through Guangzhou at any one time. Castillo cautions that firm numbers are difficult as many Africans in Guangzhou are in constant transit so the concept of residence in this context is different from the usual understanding
Link:http://en.wikipedia.org/wiki/Africans_in_Guangzhou

Apparently there are 300-500k expats in Shanghai, mainly from Taiwan and Asia. Plus a large number of students, many from the USA. They mainly live in one side of the city, alongside their Starbucks and the like.