With results in from 10 per cent of polling stations, the ANC's share of the vote in Wednesday's election stood at 42.3 per cent, with the pro-business Democratic Alliance (DA) on 26.3 per cent and the Marxist Economic Freedom Fighters (EFF) on 8.1 per cent, data from the electoral commission showed.
If the final results were to resemble the early picture, the ANC would 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.
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, its leader Cyril Ramaphosa is likely to remain the country's president, although a poor showing could make him vulnerable to a leadership challenge from within party ranks.
Cyril Ramaphosa is likely to remain president, with the ANC on track to remain the largest party. (AP PHOTO)
The ANC has won national elections held every five years since the landmark 1994 election, which marked the end of apartheid and the ascent of Nelson Mandela as president.
But since those heady days the ANC's support has declined because of disillusionment over issues such as high unemployment and crime, frequent power blackouts and corruption.
The early results showed the ANC and the DA neck-and-neck on about 34 per cent each in the key province of Gauteng, which includes the country's business capital Johannesburg and the sprawling townships of Soweto and Alexandra.
In KwaZulu-Natal, a populous eastern province where the major city of Durban is located, a new party led by former president Jacob Zuma, uMkhonto we Sizwe (MK), was performing strongly, with 41.7 per cent of the vote versus 20.1 per cent for the ANC.
Zuma was forced to quit as president in 2018 after a string of scandals and has since fallen out with the ANC leadership, leading him to throw his weight behind MK.
The party, named after the ANC's armed wing from the apartheid era, appeared to be costing both the ANC and the EFF votes, especially in KwaZulu-Natal.
By law, the electoral commission has seven days to declare full results, but in practice it is usually faster than that.
The new parliament must convene within 14 days of final results being declared and its first act must be to elect the nation's president.
This means that if the ANC is confirmed to have lost its majority there could be two weeks of negotiations to agree on how to form a new government.
