Some 4,500 African National Congress (ANC) delegates sporting bright yellow and green T-shirts gathered at an events center near Johannesburg where they will vote for a new leader on Saturday.
The start of the conference was several hours behind schedule, but a party official said that, despite the delay, voting will be on time, and results will be released around five hours later.
Cyril Ramaphosa is bidding to retain the reins of the ANC as the storied party struggles with rifts and declining support after 28 years in power.
The party's majority in parliament means that it also has control over approving the national president.
Ramaphosa's clean-hands image has been dented by allegations he concealed a huge cash burglary at his farm rather than report the matter to the authorities.
Despite this, analysts say the 70-year-old leader remains on track to win the party leadership election, expected to take place among delegates on Saturday.
"The ANC needs Ramaphosa. He will win," said political writer Ralph Mathekga. "Even those who hate him need him to win."
A victory would secure him a ticket to a fresh term as president after the 2024 elections, if his party wins that vote.
On the eve of the conference former president Jacob Zuma announced he is suing Ramaphosa over a leaked medical report linked to a 1990s arms corruption trial.
But the lawsuit is unlikely to hamper Ramaphosa's chances of securing a second term as ANC leader.
Ramaphosa won a reprieve ahead of the conference when the ANC used its majority in parliament to block a possible impeachment inquiry.
He is leading the list of only two nominated presidential candidates so far and is seen to be the most viable in the absence of better options in the 110-year-old party.
Dodging the impeachment bullet "probably strengthened his bid to seek re-election" because it removed any "immediate uncertainty," said political analyst Susan Booysen.
His rival is his former health minister Zweli Mkhize, who has corruption allegations linked to Covid-19 funds hanging over his head.
"ANC members can be dishonest but they are not idiots -- they know that Zweli Mkhize is not a bankable star," said Mathekga, author of "The ANC's Last Decade."
Ramaphosa told a party fundraising dinner Thursday night that the conference was "a watershed moment" for the ANC and South Africa.
His government has had to "steer the ship through stormy and unexpectedly rough waters," he said after listing Covid, the riots, floods and Ukraine war-induced cost of living crisis.
The ANC has also experienced its own "turbulence", he admitted. The conference will "determine where South Africa goes not only the next five years but in the next decade and beyond that," he said.
This article was compiled with data from Reuters and Agence France-Presse.