South Africa's elite police unit has raided the home of a controversial business family linked to President Jacob Zuma, as pressure increases on him to stand down.
Officials say three people were arrested as part of an investigation into the wealthy, Indian-born Guptas.
They have been accused of using their close friendship with Mr Zuma to wield enormous political influence.
Meanwhile, Mr Zuma's party has given him until the end of the day to resign.
His links to the Guptas are one of the reasons he is being forced to resign before the 2019 general election.
The Guptas and Mr Zuma deny all allegations of wrongdoing.
Pressure has been slowly increasing on Mr Zuma to stand down in recent weeks. He was expected to respond to a formal request from the African National Congress (ANC) to step down at some point on Wednesday.
However, shortly after ANC chief whip Jackson Mthembu announced that a motion of no-confidence in the president would be heard on Thursday, Mr Zuma appeared on television to say he was not prepared to stand down immediately as he had not be given good reasons as to why he should resign.
Analysis: Coincidence, or something more?
By Andrew Harding, BBC News, Johannesburg
The timing is remarkable… So why did South Africa's elite Hawks choose to move against the Guptas now? There are four possibilities:
1: This was a genuine coincidence.
The Hawks have, in recent weeks, begun to accelerate their investigation into alleged corruption at the Estina Dairy in Vrede [scroll down to read more on the allegations], with assets already seized, and prosecutions prepared, so perhaps, given the unpredictable way the political drama surrounding President Zuma is unfolding, this is just one of those serendipitous things.
2: The Hawks, with an eye on the news and the clear sense that President Zuma is losing power - and therefore any protection that the Guptas enjoyed as his friends is waning too - decided there was a risk members of the Indian-born family might flee the country.
3: The man who presumably authorised the move against the Guptas, the National Prosecuting Chief Sean Abrahams, saw the way the tide was turning against Mr Zuma (who appointed him). Mr Abrahams has been branded "Sean The Sheep" by South African media, following widespread claims that he has helped to protect Mr Zuma, the Guptas and others from corruption investigations.
Mr Abrahams, who denies the allegations, might be looking to curry favour with any new ANC-led administration.
4: Cyril Ramaphosa, or those close to him, somehow influenced the police into launching the move in a deliberate attempt to put added pressure on President Zuma. His son, Duduzane, works for the Guptas and is being talked of as a possible target of the NPA's investigations.
This would be an illegal move, but one that many South Africans now see as entirely possible, given the apparent politicisation of the justice system and the erosion of key institutions during the Zuma era.
Why was the Gupta's house raided?
According to a statement released by the Hawks - the police's elite high-priority crimes unit - the raids were carried out in connection with the Vrede farm investigation.
Three people were arrested during the raid, with two more expected to hand themselves in. According to local media, one of those arrested was a Gupta family member.
That investigation relates to the Estina dairy farm near Vrede, in the Free State, a project which was originally meant to help poor black farmers but from which the Gupta family are alleged to have pocketed millions of dollars, allegations they deny.
A tranche of leaked emails released last year alleged that some of the money ended up paying for the family's lavish wedding at Sun City, South Africa's upmarket holiday resort.
In January, the Hawks raided the offices of the Free State Premier, Ace Magashule, looking for documents linked to the project. Mr Magashule was elected secretary-general of the ruling African National Congress (ANC) in December.
Just who are the Gupta family?
The embattled Gupta family own a range of business interests in South Africa, including computing, mining, air travel, energy, technology and media.
The three brothers, Atul, Rajesh and Ajay, moved to the country in 1993 from India, just as white-minority rule was ending.
They are known friends of President Zuma - and his son, daughter and one of the president's wives worked for the family's firms.
The brothers have been accused of wielding enormous political influence in South Africa, with critics alleging that they have tried to "capture the state" to advance their own business interests.
What are the other allegations against the Guptas?
Former Deputy Finance Minister Mcebisi Jonas made a public allegation in 2016 that he was offered 600m rand ($50m; £36m) by the Gupta family to be the next finance minister - as long as he did their bidding.
It was followed by a damning report by a South African government ombudsman that accused the Guptas and President Zuma of colluding to win government contracts.
The public backlash worsened in 2017 when more than 100,000 emails were leaked which appeared to show the extent of the family's influence.
It suggested a complex web of government contracts, as well as alleged kickbacks and money laundering.
It prompted marches and public protests against the family and President Zuma, dubbed the "Zuptas".