South Africas president-in-waiting Cyril Ramaphosa will address a major ANC party rally in Cape Town Sunday as the deadlocked effort to oust scandal-tainted President Jacob Zuma grinds on.

With Zuma refusing a party request to resign, the African National Congress (ANC) has said its top decision-making committee will meet on Monday, without revealing what will be on the agenda.

The committee could recall the president from office, though he also has the constitutional right to ignore the order.

"An NEC (national executive committee) meeting is scheduled for tomorrow in Pretoria," ANC spokeswoman Khusela Diko told AFP.

Ramaphosa has said negotiations should be concluded within days, but Zuma has clung to power after rejecting a request by his party's senior officials to resign a week ago.

"As the leadership of the ANC, we've been well empowered... (we) would like to thank the congregation for their total support as we manage this transition," Ramaphosa said after a Sunday church service in Cape Town.

On Sunday afternoon, thousands of ANC supporters wearing the party's signature yellow, green and black colours gathered for the rally at the hugely symbolic Grand Parade in central Cape Town.

On the same day in 1990, Nelson Mandela spoke to euphoric crowds who filled the packed public square in front of City Hall, hours after his release from prison.

It was his first speech as free man, and a key moment in South Africa's modern re-birth as apartheid white-minority rule crumbled.

Holding the microphone for Mandela that day was a young Ramaphosa, then a trade union leader.

Zuma's presidency has been marred by corruption scandals, slow economic growth and record unemployment that have fuelled public anger in sharp contrast to national optimism after Mandela's release.

The stalemate over Zuma's departure has left South Africa in limbo, with a series of public events cancelled last week including Thursday's State of the Nation address to parliament.

Zuma's hold over the ANC was shaken in December when his chosen successor -- his former wife Nkosazana Dlamini-Zuma -- narrowly lost out to Ramaphosa in a vote to be the new party leader.

"We are in a very difficult space, and there's no doubt it requires a great deal of courage and moral strength to pass this moment," ANC deputy secretary general Jessie Duarte said Sunday.

The rally is part of ANC celebrations marking 100 years since Mandela's birth -- as well as efforts by Ramaphosa to try to revive the party's tainted reputation ahead of next year's general election.

Dispute over exit deal?

Local media said a key sticking point in the negotiations was the potentially huge legal fees Zuma is facing from prolonged court battles against multiple criminal cases.

One case relates to 783 payments he allegedly received linked to an arms deal before he came to power.

He is also reportedly seeking legal protection for his family and other associates who have been involved in controversial deals.

"Even if the ANC meeting on Monday decides Zuma needs to step down, he can still refuse because they have no legal authority," Mcebisi Ndletyana, politics professor at University of Johannesburg, told AFP.

"He is not willing to step down voluntarily. They need to close this thing early this week."

Opposition parties are calling for a parliamentary vote of no-confidence within days.

Decision time?

The ANC has insisted there will be no delay to the budget, which is on February 21.

Zuma has not spoken since being asked to resign by senior ANC officials on February 4.

But the pro-Zuma New Age newspaper said Zuma would gather his family over the weekend at his residence in Pretoria to inform them of his decision.

In 2008, the party pushed out then-president Thabo Mbeki over allegations of abuse of power.

Under Zuma, the ANC suffered its worst electoral setback since coming to power under Mandela in 1994, winning less than 54 percent of the vote in municipal elections in 2016.