Thousands of marchers are due to protest in major South African cities against President Jacob Zuma on Friday, demanding he quit after a cabinet reshuffle triggered the latest crisis of his presidency.

Zuma's sacking of respected finance minister Pravin Gordhan in the reshuffle last Thursday has outraged allies and opponents alike, undermined his authority and caused rifts in the ruling African National Congress (ANC), which has governed South Africa since the end of white-minority rule in 1994.

Rating agency S&P Global Ratings cited Gordhan's dismissal as one reason for its downgrade of South Africa to "junk" in an unscheduled review on Monday.

The rand has tumbled more than 11 percent since March 27 when Zuma ordered Gordhan to return home from overseas talks with investors, days before firing him from the cabinet.

Zuma welcomed a plan by the civil society group Save South Africa (SaveSA) to protest outside the Union Buildings, the seat of government where Zuma's offices are located in the capital Pretoria, saying it was their legal right to do so.

SaveSA is made up of civil society groups, business leaders and prominent individuals.

Mmusi Maimane, leader of the main opposition Democratic Alliance (DA) party, will lead a march in the commercial hub Johannesburg.

A "holding hands" picket is planned in Cape Town, while other groups are expected to march in coastal city of Durban.

"We call upon all South Africans, regardless of political affiliation or persuasion to join this mass action for change, where will stand together and speak with one voice that says 'Zuma must go and South Africa must come first'," Maimane said.

Many took to Twitter asking Zuma to step aside using the hashtag #ZumaMustFall.

The ANC called for peaceful marches, saying it had received reports of "people seeking to take up arms in the name of the ANC. Such behavior has no place in a democratic society".

Zuma, 74, has faced previous protests in the past. Since taking office in 2009, the president has repeatedly denied accusations of graft and senior ANC officials have backed him.

PRESSURE

On Nov. 2, Zuma faced his most recent public protest when police fired stun grenades to disperse thousands of demonstrators outside his offices in the capital.

They were demanding the release of a report by the public protector, a constitutionally mandated anti-graft official, looking into allegations that Zuma was being influenced by the Guptas, three brothers who the president says are his friends. Zuma and the Gupta brothers deny wrongdoing.

The report was released but it stopped short of reaching conclusive findings against Zuma, recommending that a judicial probe be conducted to make a determination on the allegations.

This time around, Zuma is facing political pressure for last Thursday's dismissal of Gordhan, a symbol of policymaking stability for many foreign investors. Unions, civil society groups and the opposition have all been critical, reviving pressure on him to quit.

Deputy President Cyril Ramaphosa and ANC Secretary General Gwede Mantashe also openly criticized Zuma's decision to sack Gordhan in a rare public show of discord for the party.

But after a two-day closed door meeting of senior party officials, including Ramaphosa, Mantashe and others, Mantashe told a media briefing that such public disunity was "a mistake that should not be committed again".

The ANC also rejected calls for Zuma to quit, he said and said its members in parliament would vote to defeat a motion of no-confidence against Zuma on April 18.

With this, analysts said the marches would not shake Zuma.

"Mounting opposition to President Jacob Zuma has sparked speculation that he could be forced from office," Capital Economics Africa economist John Ashbourne said in a note.

"We think that the most likely outcome is still that Mr. Zuma will decide the timing of his own exit."