Just note that the citations from the CIA world factbook is probably worthless. In the official demographics of South Africa for example, neither illegal immigration or temporary migration is noted.
This is fairly high though (as much as 3 million Zimbabweans and many people form other African countries such as Somalia).
http://en.wikipedia.org/wiki/Demographics_of_Angola#Ethnic_g...
https://www.cia.gov/library/publications/the-world-factbook/...