South Africa's ruling African National Congress (ANC) is expected to remain in power when the election commission announces formal results of national elections on Saturday.
The win will set the stage for a second five-year term for President Jacob Zuma.
On Friday, election officials said nearly all of the ballots from Wednesday's polling had been counted.
They said the results indicated the ANC had captured 62 percent of the vote. The opposition Democratic Alliance was a distant second with 22 percent.
A new party, the far-left Economic Freedom Fighters (IFP), came in third.
On Saturday, police said 59 people had been arrested late Friday in a Johannesburg township where IFP supports alleged election fraud. Angry demonstrators in Alexandria burned tires and set up road blocks.
The South African Press Association said Saturday that IFP leader Julius Malema urged supporters to accept the polling results, saying "no election was perfect." The news agency says he also said that anyone who voted for the ANC had contributed to "corruption and degradation within the country."
The ANC has won every election since South Africa's first democratic polls in 1994, after the end of apartheid.
But, critics have assailed the party for corruption scandals and for what they view as its failure to enact programs that would lift millions of black South Africans from poverty.
In spite of criticism, many voters remain loyal to the party that was led by Nelson Mandela and was largely responsible for ending white minority rule.