The ANC has won more than 60 percent of the vote at every election since Nelson Mandela was sworn in as the country’s first black president in 1994.
But 22 years after the fall of white-minority rule, a faltering economy, rampant corruption and soaring unemployment have eaten into the party’s popularity.
Millions of voters braved a vicious cold snap to queue outside polling stations Wednesday, bringing an end to a campaign marked by disputes over alleged racial slurs.
Polls leading up to the vote had the main opposition Democratic Alliance (DA), which controls Cape Town, trouncing the ANC in the capital Pretoria, economic powerhouse Johannesburg and seaside Port Elizabeth.
But a final Ipsos survey earlier this week placed the ANC slightly ahead, as previously undecided voters climbed down from the fence.
“ANC support tends to increase in the last days of election campaigns as unhappy supporters, who have insisted they will vote for the opposition or stay home, start to inch back the closer they get to polling day,” political analyst Steven Friedman wrote on Wednesday in local daily Business Day.
“In previous elections, most returned to the ANC in the polling booth.”
Both the ANC and DA will likely find themselves forced to court smaller parties and independent candidates to cobble together outright municipal majorities.
“If I was to predict, I would say the DA has a better chance at forming a winning coalition in Port Elizabeth, and the ANC in Pretoria,” independent analyst Daniel Silke told AFP.
“Johannesburg could very well see the ANC scrape through with just over 50 percent for an outright win.”
Contesting its first local election after it burst onto the scene ahead of the 2014 general vote, the far-left Economic Freedom Fighters may find itself playing kingmaker.
A record 26.3 million people registered to choose mayors and other local representatives responsible for hot-button issues including water, sanitation and power supplies.
The local vote is also seen as a mid-term reflection on the performance of the ANC and the leadership of President Jacob Zuma, who has been plagued by scandal since he took office in 2009.
Even if the ANC maintains its hold on power through inter-party alliances, any overall drop in support would be a loss, said Silke.
“Simply to form a coalition in Pretoria, the capital, would be an embarrassment.”
“What it really will say is that few results are certain in South African politics any more, that the certainty the ANC has enjoyed for so long would simply be negated.”
South Africa’s electoral commission said late on Wednesday voting proceeded smoothly and without major incident.