After polling stations officially closed, electoral officers said hundreds of people still in queues would be allowed to vote.
The ANC looked certain to capitalise on its enduring appeal as the party that ended white rule and the only questions were the size of its victory and whether it could make a clean sweep of all nine provinces.
Long queues snaked from many of the 17,000 polling stations through the day, a confirmation that the 20 million registered voters still cherish the right to vote 10 years after Nelson Mandela first swept the ANC to power in multiracial elections.
"We hear that some people were at (polling) stations at five o'clock. Both young and old -- it's fantastic," said Brigalia Bam, head of the Independent Electoral Commission.
"This is what we fought for," declared Winnie Madikizela-Mandela, former wife of Mandela, as she voted in Johannesburg's Soweto black township.
"We are absolutely certain of an enormous victory," added Madikizela-Mandela, a popular ANC figure.
Police said they arrested 43 armed former soldiers on Tuesday night as they apparently met to discuss plans to disrupt voting in volatile KwaZulu-Natal province.
The former members of the South African army would appear in court on Thursday charged with holding an illegal meeting and planning to disturb the peace.
Polling passed generally peacefully in KwaZulu-Natal and South Africa's eight other provinces despite complaints by some voters they had been in line for as long as 10 hours.
A close contest between the ANC and the Zulu-based Inkatha Freedom Party (IFP) had raised fears of violence in the province, where 20,000 police were deployed.
As Mbeki heads toward a second term in office, he faces increasing pressure to deliver on his pledges to turn the tide on AIDS, a big killer in South Africa.
"I sincerely hope that the entire world will abandon violence and use peaceful methods of asserting their rights as citizens"
Former SA president
He is also pressed to tackle unemployment, officially at 31% and alleviate back-breaking poverty as the euphoria gives way to more concrete demands for a better life.
South Africa's first black president and hero of the anti-apartheid struggle, Nelson Mandela, turned up at the ballot box in the upscale Johannesburg borough of Houghton and declared:"I feel elated as I am able to vote again."
"I sincerely hope that the entire world will abandon violence and use peaceful methods of asserting their rights as citizens," the 85-year-old former leader appealed.
Mandela on Wednesday was accompanied by the head of South Africa's election commission, Brigalia Bam, who reminisced about the 1994 elections, the country's first all-race ballot.
"Ninety-four will remain for us something we will never forget, especially for people of my generation because we never thought we would live to see this man out of prison" and casting his vote, she said of Mandela.
Bam also said voter turnout was high and "some people have been queing from the early hours of the morning".
In the sprawling black township of Soweto outside Johannesburg, hundreds of people queued outside voting stations, while large crowds gathered at polling spots from Cape Town to Durban.
Voters waiting since early morning
to cast their ballots
Attention has focused on the restive province of KwaZulu-Natal, where the ruling party faces one of its sharpest local challenges from the Zulu-based Inkatha Freedom Party (IFP).
The ANC has vowed to wrest control of the province from the IFP, and while campaigning has been largely peaceful there have been sporadic reports of political violence.
Hundred of troops and up to 20,000 police were out in force in the province, concentrated in the rural area of Ulundi, the coastal resort of Durban and nearby KwaMashu - all described as potential flashpoints for violence.
Only a handful of people have died in politically-motivated killings in KwaZulu-Natal this year, compared to scores in the last poll in 1999 and an estimated 20,000 in 1994.
Of the 45 million population, more than 20 million are eligible to vote for a 400-member National Assembly, which will meet next week to choose a president.
Nine provincial assemblies will also be elected on Wednesday and will in turn select delegates to the 90-member National Council of Provinces, parliament's second chamber.