Police fired more rubber-coated steel bullets at a crowd of anti-immigrant protesters in downtown Johannesburg on Friday afternoon, as they tried to separate the protesters from a group of immigrants.
In Gauteng province, of which Johannesburg is the capital city, police arrested 18 people after overnight street battles, Major General Phumzo Gela, deputy police commissioner, said on Friday afternoon.
Earlier on Friday, police clashed with a crowd of South Africans in Johannesburg's Jeppestown area.
The crowd carrying hammers and axes gathered near the city centre, chanting "Foreigners must leave."
Groups of South Africans in Jeppestown and Cleveland blocked roads with rocks and burning tires and then ordered foreigners to leave the country, police said.
Jeppestown and Cleveland are neighborhoods adjoining the Johannesburg Central Business District (CBD), Al Jazeera reported.
A number of shops in the CBD were reported to have been looted and vandalized, further escalating tensions between foreigners and South Africans in Johanneburg.
Police said the suspects were trying to break into shops owned by foreigners.
Colonel Dlamini, police spokesperson, told Al Jazeera that calm had been restored, but refused to reveal whether police had received credible reports of further threats of violence against foreigners in the city.
Violence targeting immigrants started earlier in April in the port city of Durban, claiming the lives of six people so far.