The African National Congress appeared on course to lose the parliamentary majority it has held for 30 years, partial results from South Africa's national election showed, in what would be the most dramatic political shift since the end of apartheid.
If the final results confirm the loss of its majority, the ANC will be forced to make a deal with one or more other parties to govern - a situation that could lead to unprecedented political volatility in the coming weeks or months.
"There will be checks and balances on the ANC power, but the ultimate risk is that the infighting could make governance ineffective," said Simon Harvey, head of foreign exchange analysis at Monex Europe.
With results in from 16.7% of polling stations, the ANC's share of the vote in Wednesday's election stood at 42.5%, with the pro-business Democratic Alliance (DA) on 25.8%, data from the electoral commission showed on Thursday.
The Marxist Economic Freedom Fighters (EFF) party was on 8.5%, while uMkhonto we Sizwe (MK), a new party led by former president Jacob Zuma, was snapping at its heels on 8%.
"I don't think it's likely for the ANC to reach a majority," said pollster Reza Omar of Citizen Surveys, noting that while the picture would evolve, it was unlikely to change to that extent.
South African broadcaster eNCA projected that the ANC's final score would land on the 45% mark while the DA would remain the largest opposition party on 21%.
"The ANC looks forward to a clear mandate from voters to continue the work of transforming South Africa and building a better life for all," the party said in a statement.
Tessa Dooms, director of the Rivonia Circle think-tank in Johannesburg, said the early results were skewed towards rural areas where she would have expected the ANC to be performing more strongly than it was.
"The rural vote comes in early and it's always much smaller. The urban vote comes in quite late. I think this election will be a lot more contested in the urban areas," she told Reuters at the results centre in Midrand, north of Johannesburg.
Under South Africa's constitution, the newly elected National Assembly will elect the next president. With the ANC still on course to be the largest party, that is likely to be its leader Cyril Ramaphosa, the incumbent.
However, a poor showing could make him vulnerable to a leadership challenge from within party ranks, whether in the immediate future or at some point during his term.
With South Africa entering uncharted political territory, Harvey said the speed at which a coalition could be formed would be an indication of what was to come.