South Africa's ruling African National Congress (ANC) has won another term in power, but with its lowest-ever vote share at 57.5 per cent, according to the electoral commission.

The official website on Saturday showed the ANC with the largest vote share after 100 per cent of the ballots had been counted in all 22,925 districts. The vote took place earlier this week.

The ANC's main challenger, the Democratic Alliance (DA), was on 20.8 per cent. The radical Economic Freedom Fighters (EFF) nearly doubled its result from the last elections, winning 10.8 per cent.

DA leader Mmusi Maimane pledged on Friday to ‘bring change’ at the next national polls in 2024.

The final result is expected to be formally announced at 6 pm (1600 GMT).

 With more than 17.6 million votes cast in Wednesday's vote, nearly 66 per cent of eligible voters, South Africa's voter turnout is steadily declining. In 2014, 73.4 per cent of the electorate cast their ballots, while in 2009, voter turnout stood at 77.3 per cent.

In the months running up to the election, political parties and the commission canvassed voters under the age of 25. Youth groups say young voters feel excluded from South Africa's political class, which is dominated by liberation movements born out of the apartheid era.

The commission also counted 235,449 spoilt ballots. The reason for this relatively high figure is still unknown. Analysts say it could range from voter apathy to confusion over an unusually long ballot paper. A record 48 parties contested the national election.

The election was marred by accusations of voter irregularities from smaller parties. In a televised press conference on the floor of the national results centre in Pretoria, smaller parties banded together late Friday, saying they may challenge the Independent Electoral Commission's result due to concerns over double voting.

On Thursday, local press reported that more than 20 people were arrested for voting twice. In a televised press conference on Saturday, the electoral commission said that it would investigate the incidents, but would not delay releasing the result over the matter.

South Africa has been reeling from almost a decade of corruption scandals under former president Jacob Zuma, who was forced to resign last year and is currently on trial.

The ANC's President Cyril Ramaphosa, who replaced Zuma, has promised a ‘new dawn’ for the country.