Voting for the new leader of South Africa's governing African National Congress (ANC) party was almost complete on Monday, as the race pitting President Cyril Ramaphosa against former health minister Zweli Mkhize entered the final stretch.

Counting of votes was due to start within hours, with the winner expected to be announced later on Monday.

Ramaphosa had been widely tipped to secure re-election for a second five-year term at the ANC gathering in the country's biggest city Johannesburg, but analysts say the contest is shaping up to be closer than predicted.

Ramaphosa secured more than twice the nominations that Mkhize did before the leadership conference from rank-and-file ANC members, but local media have reported that some provincial voting blocs were considering shifting their allegiance to Mkhize during horse-trading on Sunday.

William Gumede, head of the Democracy Works Foundation think tank, wrote in a LinkedIn post that the vote was "going to the wire - and will likely be decided by a handful of votes".

François Conradie, lead political economist at Oxford Economics, said a Mkhize win would rock the country as he is seen as closer to a faction loosely aligned with former President Jacob Zuma which favours a more rapid transfer of wealth into the hands of South Africa's Black majority.

"If Mr Ramaphosa wins, it will be by making some compromises with that same Radical Economic Transformation faction, casting a pall on the economic outlook anyway," Conradie said in a research note.

Ramaphosa's re-election campaign has been dogged by the "Farmgate" scandal that broke in June involving large sums of foreign currency found hidden at his private game farm.

Ramaphosa has denied wrongdoing and not been charged with any crimes over the scandal, but it has raised questions about how he acquired the money and whether he declared it.

Mkhize was health minister during the COVID-19 pandemic, until Ramaphosa put him on special leave last year over after allegations his department irregularly awarded contracts to a communications company controlled by his former associates.

Mkhize has denied wrongdoing over the contracts.

He campaigned for the ANC leadership during the party's last leadership contest in 2017, losing out to Ramaphosa.