The South African rand plunged more than five percent after President Jacob Zuma sacked his finance minister, a man widely seen as a competent manager of one of the world's most important emerging economies.
Finance minister Pravin Gordhan was ousted and ten new cabinet appointments made in a dramatic reshuffle that could split the ruling African National Congress, which led the fight against apartheid and came to power under Nelson Mandela in 1994.
The late-night move caused the rand to drop as low as 13.5 to the dollar, down from 12.8, as investors reacted to concerns that Zuma, who has been tainted by corruption scandals, had secured a free hand over government finances.
Gordhan was replaced by home affairs minister Malusi Gigaba after a months-long battle with Zuma over government spending.
The president said in a statement that the changes were "to bring about radical socio-economic transformation and to ensure that the promise of a better life for the poor and the working class becomes a reality."
In his power struggle with Zuma, Gordhan was supported by several ministers and many international investors, as well as being widely admired by ordinary South Africans and veterans of the anti-apartheid struggle.
He campaigned for budget discipline and against corruption, but Zuma's allies have accused him of thwarting the president's desire to enact radical policies supposed to tackle racial inequality.
- Choosing a successor -
Zuma is due to step down as head of the party in December, ahead of the 2019 general election.
He is seen as favouring his ex-wife, former African Union chief Nkosazana Dlamini-Zuma, to succeed him, ahead of Deputy President Cyril Ramaphosa.
"Zuma's opponents in the ruling party are likely to use Gordhan's removal to launch a preemptive strike against Zuma and try to win back control of the ANC," the Eurasia consultancy said in a note.
"Longer-term, the ANC will have a hard time recovering from this period of intense instability."
The ANC, which was banned under white-minority rule, has lost popularity in recent years due to corruption allegations, record unemployment and slow economic growth.
The reshuffle was reportedly delayed due to the death of celebrated anti-apartheid activist Ahmed Kathrada.
Kathrada was a fierce critic of Zuma, and his funeral on Wednesday became an impromptu rally against the president, who did not attend at the request of the family.
Gordhan, 67, was given a standing ovation at the event.
- Legal troubles -
The main opposition Democratic Alliance party said Zuma had "bowed to the whims of those who are determined to enrich themselves at the expense of the poor and jobless".
The president is accused of being in the sway of the wealthy Gupta business family, allegedly allowing them influence over government appointments, contracts and state-owned businesses.
"We view this as an open attack on Treasury to replace people who are conservative and anti-corruption with people loyal to Zuma," said Peter Attard Montalto, analyst at Nomura bank, after the reshuffle.
"Zuma is taking a risk here and the next step is to watch what happens with resignations."
Sports minister Fikile Mbalula was moved to head the police department, while anti-apartheid veteran Derek Hanekom was sacked as tourism minister.
Earlier Thursday, the leftist opposition Economic Freedom Fighters (EFF) party filed a request for the Constitutional Court to institute impeachment proceedings against Zuma.
The court last year found him guilty of violating the constitution after he refused to repay taxpayers' money used to refurbish his private rural house.
Zuma is also fighting a court order that could reinstate almost 800 corruption charges against him over a multi-billion dollar arms deal in the 1990s.
In late 2015, the president reluctantly re-appointed Gordhan, who had served as finance minister from 2009 to 2014, to calm panicked markets after sacking two finance ministers within four days.