South Africa's ruling ANC kicked off what promises to be a contentious five-yearly party conference Sunday, with embattled President Jacob Zuma facing a leadership challenge from his number two.

Thousands of singing and dancing ANC members clad in party colours and regalia descended on the city of Bloemfontein for the five-day conference, which will go a long way toward deciding who will lead South Africa until the end of the decade.

Deputy President Kgalema Motlanthe is hoping to wrest control of the party from Zuma.

Should he succeed, the ANC's commanding electoral standing means he is almost certain to become the country's next president.

But Zuma -- despite being marred in a series of financial scandals and leading the party to its most serious crisis in decades -- is expected to prevail.

Preliminary voting has put the incumbent well ahead of his rival in the leadership stakes, and he remains the odds-on favourite to remain in power after the 2014 elections.

But with the party in the kind of crisis seldom seen since it was banned by the apartheid government in 1960, Zuma could be in for a rocky ride.

The conference will cap a horrendous year for the storied revolutionary movement.

Despite the cadres' best efforts, 12 months of celebrations to mark the party's 100th year have been drowned out by allegations of corruption, flashes of authoritarianism and economic mismanagement which critics say borders on gross negligence.

Zuma is expected to address some of those issues in a speech later Sunday, before candidates for key party posts are named.