A police spokesman said on Saturday that the police used rubber bullets and stun grenades to disperse protestors in the impoverished Alexandra area who had burned tyres and barricaded roads, Brigadier Neville Malila told Reuters.
Alexandra was "calm this morning," Malila added. Earlier, broadcaster eNCA reported the army had been deployed overnight to restore order. It was not immediately clear if the army remained in the area.
The protests were sparked after as many as 400 people had gathered on Friday outside a court in Alexandra to demand the release of other protestors arrested a day earlier, Malila said.
South Africa's ruling African National Congress won the 2014 national election with 62.16 percent of the votes, the electoral commission said on Friday.
Although the party remains popular with South Africa's black majority after dismantling the apartheid system is 1994, there is also growing discontent among the millions who remain mired in grinding poverty.