South Africa's ruling African National Congress is preparing to celebrate its win in national elections, with the formal announcement coming later on Saturday.

With 99.9% of votes counted, the ANC has 57% of the vote. It is the worst-ever showing at the polls for the party of the late Nelson Mandela, which has ruled South Africa since the end of apartheid 25 years ago.

Voter turnout is another low at 65%, reflecting the frustrations of many South Africans after corruption scandals around the ANC that led to the ouster of former president Jacob Zuma last year.

Current President Cyril Ramaphosa, a Mandela protege, has vowed to clean up the rot and apologized to South Africans. But his new five-year term is threatened by Zuma allies within the ANC's leadership.