Early vote tallies suggest South Africa's ruling ANC party will retain power, but analysts say its share of the vote could fall below 60 percent for the first time since the end of white minority rule.
As of late Thursday morning, more than 4 million votes had been counted out of about 26.8 million registered voters.
In the parliamentary vote, the ANC was on 55 percent, with the main opposition Democratic Alliance (DA) on nearly 26 percent and the leftist Economic Freedom Fighters (EFF) on nearly 9 percent.
South Africans voting for a new parliament and nine provincial legislatures had expressed frustration at rampant corruption, high unemployment and racial inequalities that persist 25 years after Nelson Mandela's former liberation party swept to power in the first all-race poll in 1994.
Based on the early results, the News24 online site predicted the ANC would win between 56 percent and 59 percent of the final vote.
The news organisation's election analyst Dawie Scholtz said the ruling party's vote share had been dragged down by lower turnout and declining support among the black majority.
"Lower black voter support is a big problem for the ANC. That is shown by our numbers in Gauteng and KwaZulu-Natal. In 2014, the ANC secured 80 percent of black voters, but it seems like this year they will end up on 75 percent," he said.
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The Council for Scientific and Industrial Research, a government agency, also forecast a substantial decline in support for the ANC. It predicted the ANC would get just over 57 percent in the parliamentary vote and closer to 50 percent in the provincial polls.
Turnout stood at just over 65 percent, according to the votes processed so far, the electoral commission said.
The elections are the first barometer of national sentiment since President Cyril Ramaphosa replaced scandal-plagued Jacob Zuma as head of state in February 2018.
Ramaphosa is trying to arrest a slide in support for the ANC, which has won every parliamentary vote since the end of apartheid in 1994 but whose image has been tarnished by corruption scandals and a weak economy in the past decade.
Elections officials said voting had in general progressed smoothly but that there had been isolated incidents where bad weather, unscheduled power outages or community protests had caused disruptions.
The ANC's support has fallen under Zuma and it lost control of big cities like the commercial capital Johannesburg in local government elections in 2016.
The ANC now controls eight of the country's nine provinces, with the DA in power in the Western Cape. Analysts predict the provincial races for Gauteng, where Johannesburg and theamnistrative capital Pretoria are located, and the Western Cape, home to Cape Town, will be close.
Ramaphosa, who became ANC leader in December 2017 after narrowly defeating a faction allied with Zuma, has promised to improve poor public services, create jobs and fight corruption.
But he has been constrained by divisions within his own party, where some Zuma supporters still retain influence and oppose his agenda.