South Africa's governing ANC is set to elect a successor to President Jacob Zuma in a leadership vote by a party that has ruled since the end of apartheid but lost its lustre in a welter of scandal and corruption allegations.

Whoever emerges at the helm of the African National Congress, a 105-year-old liberation movement that dominates Africa's most industrialized economy, is likely to become the next president after elections in 2019.

After long delays on the first day of the ANC conference on Saturday, the leadership contest remained too close to call. Most grassroots delegates backed Deputy President Cyril Ramaphosa, 65, or Zuma's preferred candidate, his ex-wife Nkosazana Dlamini-Zuma, 68.

The election is perhaps the most pivotal moment for the ANC in its 23 years of power. Scandal and graft accusations have tainted Zuma's presidency and the party that launched black majority rule under Nobel Peace Prize laureate Nelson Mandela is now deeply divided, its image tarnished at home and abroad.

Ramaphosa drew the majority of nominations from party branches scattered across the country. But the complexity of the leadership race means it is far from certain he will win when the votes are finally counted.

South Africa Leadership Fight

Front-runner and Deputy President Cyril Ramaphosa looks on at the start of the ruling ANC elective conference in Johannesburg on Saturday. (Themba Hadebe/Associated Press)

Owing to the delays, the final result is now expected only on Monday.

"We hope to start voting at some point later this afternoon and have those results, as it now stands, possibly by tomorrow morning," said ANC Deputy Secretary General Jessie Duarte. "We don't rush results; we would like them to do a thorough and proper job."

ANC spokesperson Khusela Sangoni said the party had completed vetting the eligibility of roughly 6,000 delegates to decide who would take part in the voting.

'It is going to be very close'

The ANC said 4,776 delegates of the more than 6,000 attending the conference would be allowed to vote in the tight race. "Credentials are the make and break of the conference," she said.

As well as electing a new leader, the ANC will choose senior officials such as the secretary general and members of the National Executive Committee. It will also set policy priorities for the run-up to the 2019 election.

Formal nominations of Ramaphosa and Dlamini-Zuma and candidates for other positions was due to start later on Sunday.

Under ANC rules, a majority of nominations is not the same as the most votes at the conference and delegates are not bound to vote for a particular candidate.

How the delegates do cast their ballots may also be subject to vote-buying and intimidation — widely acknowledged to have swayed previous leadership contests.​

"It is going to be very close," a senior ANC source said. "Both camps have spreadsheets where they have calculated the number of delegates on their side. Both sides have different assumptions and guesswork."

South Africa Leadership Fight

Front-runner and ex-wife of President Jacob Zuma, Nkosazana Dlamini-Zuma, waits for the delayed start of the ruling ANC elective conference in Johannesburg on Saturday. (Themba Hadebe/Associated Press)

Dlamini-Zuma pledged during her campaign to tackle the racial inequality that persists in South Africa since the end of white minority rule. Ramaphosa has vowed to fight corruption and revitalize the economy. That message has gone down well with foreign investors.
In a boost to Ramaphosa, courts ruled that officials from some provinces seen as supporting Dlamini-Zuma had been elected illegally and were barred from the conference.

Troubled tenure

In his last speech as ANC leader on Saturday, Zuma announced plans to raise subsidies to tertiary colleges and universities, a move analysts said was timed to appeal to the more populist members of the party.

He also lashed out at members of the ANC who turned to the courts to resolve party issued and called on the party to unite behind whoever is declared the winner, saying: "The movement (ANC) must be the winner and not individuals."

Zuma, who has been head of state since 2009 and ANC leader since 2007, has faced accusations that have damaged the ANC's stature and caused sharp internal rifts.

The allegations have included undue influence in making cabinet appointments and awarding state tenders to his friends, the wealthy Gupta family. Zuma and the Guptas have denied any wrongdoing.

In August, Zuma narrowly survived another attempt in parliament to force him from office after some members of his party voted with the opposition in a no-confidence vote.