Some 5,000 delegates will be able to vote in the leadership contest
South Africa's governing African National Congress (ANC) is holding its party congress at which members will vote for its next leader.
President Jacob Zuma is being challenged for the top job by his deputy, Kgalema Motlanthe.
The congress, held every five years, is taking place in Manguang, where the party was formed a century ago.
Correspondents say the party is battling to regain the moral high ground, amid accusations of corruption.
Some 5,000 delegates are eligible to vote at the 53rd National Conference, which will last for five days.
Mr Zuma will open proceedings with an address to the delegates on the current political landscape in South Africa.
The president is confident he can win a second term, says the BBC's Milton Nkosi in Manguang, despite media coverage of his personal life and allegations that he misused public funds to renovate his private home.
But Deputy President Motlanthe was nominated by at least three of South Africa's nine provinces and is hoping for a surprise victory. He only confirmed his candidacy last week.
If Mr Motlanthe is appointed, the ANC's control of parliament means he will almost certainly become South Africa's next president in elections in 2014.
The results of the leadership contest are expected later this week.
The ANC will use the congress to try to shake off persistent accusations of corruption and infighting, says our correspondent.
It is also lagging in delivering meaningful change for millions of poor South Africans, as it promised when it came into power at the end of apartheid in 1994, he adds.