ANC deputy secretary general Jessie Duarte said the election showed voters want an ANC that remains true to the values and principles on which it was founded.
This as the party won the elections with 57.5% of the vote, provisional results showed after votes were counted from all provinces.
Saturday's win assured a sixth straight term in power for the ANC. But the result was the worst-ever electoral showing for the party, which has ruled South Africa since the end of apartheid 25 years ago.
Support for the ANC, which gained 62% in the previous election in 2014, has steadily declined since it took a record 69% of the vote in 2004. Saturday's electoral showing comes amid growing voter frustration over rampant corruption and high unemployment.
President Cyril Ramaphosa, who replaced Jacob Zuma last year, now faces the challenge of regaining public confidence in a party that remains beset with internal divisions and oversaw a raft of economic crises.
Jessie Duarte, ANC deputy secretary general, said the party will move swiftly to counter corruption and increase economic growth.
"We need to correct our mistakes," she said, adding that the election showed voters want an "ANC that is united and in its unity remains true to the values and principles on which it was founded".
The result will also renew pressure on Ramaphosa to decisively deal with Cabinet ministers accused of corruption.
"The real test is whether such individuals will face prosecution," said Phephelaphi Dube, a constitutional expert.
The elections commission will formally announce the official results later on Saturday.
'Turned on by politics'
Meanwhile, the opposition Democratic Alliance also experienced a two percent dip from 2014, though it maintained its grip on the Western Cape province, which includes the city of Cape Town.
The results showed significant gains for the far-left Economic Freedom Fighters (EFF), which, with almost 11% of the vote, polled about five percentage points higher than in its first election in 2014. The EFF is now the official opposition in three out of South Africa's nine provinces.
On the other side of the political spectrum, there were notable advances for the right-wing Freedom Front Plus.
Despite a number of interruptions and claims of electoral fraud and insufficient ballot papers at certain voting stations across the country, international and domestic election observers have endorsed the elections as free and fair.
Overall voter turnout stood at 65%, with more than half of eligible voters under 30 years of age failing to register to vote.
Sheila Meintjes, an associate professor of political studies at the University of Witwatersrand in Johannesburg, noted that the overall turnout was higher than in a number of recent elections in Western countries including the US and the UK.
"This shows that we're still a country that is turned on by politics," she told Al Jazeera.
But Tumi Jonas, a 32-year-old academic based in Cape Town, who voted for the radical Black First Land First, one of a number of new small parties on the ballot, said the election had "felt like an empty spectacle".
"This is my third time voting, and I've never felt so despondent about the whole thing. It's just going to be more of the same. I'm not feeling very hopeful about the future. I don't think our electoral system is really working for a lot of people," Jonas said.
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