Residents looted shops owned by foreigners on Thursday, with one Somali shopkeeper now fighting for his life.
Hundreds of people from Malawi, Burundi, Zimbabwe and Congo have reportedly fled their homes in the past two weeks.
A police spokeswoman was quoted as saying that several arrests have been made.
The rioting followed comments by Goodwill Zwelithini, king of the Zulu ethnic group and figurehead of the eastern province of KwaZulu-Natal, who criticised the presence of immigrants in South Africa.
Zwelithini later said his comments had been misinterpreted and that he had only criticised high crime levels, according to a local broadcaster.
More than 60 people died in xenphobic attacks that swept the country in 2008.
Economically disadvantaged South Africans see foreigners as competing with them for businesses and jobs. (dpa/NAN)