African National Congress (ANC) deputy leader Kgalema Motlanthe was due to be sworn in as South Africa's third president since democracy in 1994 on Thursday, five days after Thabo Mbeki was forced out of the job by his party.

Mbeki's nine years as president, which followed Nelson Mandela's single five-year term, formally came to an end at midnight on Wednesday. He chaired his last cabinet meeting on Wednesday.

Mbeki resigned on Sunday at the demand of the ANC over a court finding of political interference in ANC leader Jacob Zuma's prosecution for corruption.

Motlanthe, a former union leader and ANC secretary general under Mbeki, is the ANC's choice to replace Mbeki until general elections scheduled for April or May, after which ANC leader Jacob Zuma is expected to become president.

The National Assembly held a special sitting Thursday to elect a new president. The ANC's more than two-thirds majority in parliament means Motlanthe is almost certain to defeat Joe Seremane, the candidate of the main opposition Democratic Alliance (DA).

The DA, who have described Motlanthe as a good candidate, indicated it was nominating party chairman Seremane to have a semblance of a contest.

Motlanthe, an ANC moderate and minister in the presidency, has acted as a bridge between the Mbeki-led government and the pro-Zuma ANC leadership.

Analysts say the self-effacing former secretary-general of the National Union of Mineworkers, who spent 10 years in prison on Robben Island for resisting apartheid, is a good choice to try to ease jitters in South Africa over the political upheaval.

One of his first tasks will be to constitute a cabinet, after a third of Mbeki's cabinet - 11 ministers and three deputy ministers - resigned on Tuesday.

The ANC confirmed Thursday that parliament speaker Baleka Mbete would become deputy president after Mbeki's deputy Phumzile Mlambo-Ngcuka, resigned.

Around half of the resigning ministers did so as a matter of procedure because they wanted to be formally appointed ministers by Motlanthe.

Finance Minister Trevor Manuel, one of the world's longest-serving and most popular finance ministers, was among those who quit but later confirmed he was available to serve Motlanthe.

In his farewell letter to his cabinet, which was published Thursday, Mbeki said he believed history would judge him kindly.

"I trust that, in time, history will hand down the judgment that when we, as our country's national executive, were given the opportunity, we lived up to the expectations of the masses of our long-suffering people to serve them as honest and selfless leaders - men and women of conscience."