South African police have issued a "red alert" at the country's borders for Zimbabwe's First Lady Grace Mugabe, the police minister has said.
She is accused of hitting a 20-year-old woman over the head with an extension cord in a hotel room near Johannesburg.
Police expected Mrs Mugabe, 52, to turn herself in on Tuesday, but she failed to show up.
The first lady's whereabouts are not known but she is believed to still be in South Africa.
Zimbabwean President Robert Mugabe is now also in the country ahead of a southern African heads of state meeting due to start on Friday.
Mrs Mugabe has not commented on the allegation.
Police Minister Fikile Mbalula said: "We, in terms of South African police, [have] already put tabs on the borders in relation to her leaving the country, so there is no question about that.
"So tabs have been put, a red alert has been put, so she is not somebody who has been running away."
On Wednesday, South Africa's police ministry said Zimbabwe's government had sought diplomatic immunity for Mrs Mugabe.
Meanwhile, South African lawyer Gerrie Nel, who successfully prosecuted Paralympic athlete Oscar Pistorius, is supporting the woman making the allegation, Gabriella Engels.
Mr Nel is now working with the Afriforum group, which mainly lobbies for the rights of Afrikaners in South Africa.
Afriforum said if the police failed to act in the case then it would take up a private prosecution.
It also said that it would fight any move to grant Mrs Mugabe diplomatic immunity.
Ms Engels told the BBC that she was attacked by Mrs Mugabe who believed she knew the whereabouts of her son, Bellarmine.
"We kept telling her 'we do not know where he is... we haven't seen him for the night'... She cornered me… and started beating the hell out of me.
"That's when she hit me with the plug and the extension cord. And I just remember being curled down on the floor with blood rushing down my face and down my neck.
"She hit us with so much hate."
Ms Engels has now laid an assault charge and added that she wants Grace Mugabe to "go to jail".
Zimbabwe's first lady, Grace Mugabe, is due in court in South Africa following allegations of an assault, South Africa's police minister says.
She has "handed herself over to the police" but is not under arrest, Fikile Mbalula said.
South African model Gabriella Engels, 20, has accused Mrs Mugabe of hitting her on the head with an extension cord during a confrontation at a hotel.
She released an image of a face injury online. Mrs Mugabe has not commented.
Ms Engels accused Mrs Mugabe, 52, of hitting her after finding her with her two sons in a hotel room in Sandton, a plush suburb north of Johannesburg, the BBC's Pumza Fihlani reports.
The attack is said to have happened on Sunday evening.
In a phone interview for South Africa’s News24 news site, she said: "When Grace entered I had no idea who she was. She walked in with an extension cord and just started beating me with it.
"She flipped and just kept beating me with the plug. Over and over. I had no idea what was going on. I was surprised… I needed to crawl out of the room before I could run away.
"Her ten bodyguards just stood there watching, no-one did anything, no-one tried to help me."
"There was blood everywhere," she added. "Over my arms, in my hair, everywhere."
In a statement, they confirmed that on Monday an unnamed 20-year-old South African woman had registered a "case of assault with intent to do grievous bodily harm".
She was "allegedly assaulted by a prominent woman at a hotel in Sandton," they said, without naming Mrs Mugabe.
Who is Grace Mugabe?
A man held hostage by al-Qaeda for nearly six years has said he thought it was a "joke" when he was freed.
Stephen McGown, 42, who has South African and UK nationality, was kidnapped from a hotel in Timbuktu, in Mali, along with two others in 2011.
He was released on 29 July following "efforts" from South Africa's government and other authorities.
Mr McGown told a press conference he had tried to keep up routines while in captivity to stay positive.
Speaking for the first time since his release, Mr McGown said he had been in a car with one of his captors when he was told he could leave.
He said he had assumed the man was "joking" and was still not convinced he was free after leaving the vehicle and getting into a second car that was waiting for him.
It was only later in the journey that it sunk in that he was free.
"It was quite a moment," he said.
"It's difficult to actually understand, comprehend, because there have been so many ups and downs over the last five-and-a-half years.
"You're not sure who you can and who you can't believe...
"You want to believe, but you're tired of really coming down with a bang after they tell you you should be going home soon."
Mr McGown said he did not believe his captors knew his nationality when they caught him but had wanted him to be from the UK because British captives were more valuable to them.
He said he had converted to Islam while captive and that he focused on remaining positive in captivity because he did not want to come home "a mess".
"I suppose you try and find routines, you try and find things that sort of give you an escapism from the situation, like doing a bit of exercise," he said.
"I was trying to make conversation with the mujahideen [people who engage in Jihad] to get along with the mujahideen. I didn't want to come out an angry person."
Mr McGown also paid tribute to his mother, who died in May, saying she was "an amazing lady and I can imagine the difficulties she went through".
He added that he did not know why he had been released.
Authorities have previously said that Mr McGown was released following efforts by the South African and Swedish governments and the NGO Gift of the Givers.
The South African government previously said no ransom was paid for Mr McGown's release.
South Africa's President Jacob Zuma has survived his latest vote of no confidence - despite the ballot being held in secret.
Opposition parties had hoped the secret ballot would mean some MPs from the governing ANC party might side with them against the president.
But the motion, called amid repeated allegations of corruption, was defeated by 198 votes to 177.
This news was greeted with cheers and singing by ANC MPs.
Speaking afterwards, Mr Zuma said he had come to thank his supporters and "those in parliament who had voted correctly".
"They believe they could use technicalities in parliament to take over the the majority from the ANC," he told the assembled crowd.
"It is impossible: they cannot. We represent the majority."
Mr Zuma has found himself embroiled in a number of scandals since taking office in 2009, including using taxpayer money for upgrades on his private home, and becoming too close to the wealthy Gupta family, who are accused of trying to influence politician decisions.
Both Mr Zuma and the Gupta family deny wrongdoing.
Criticism increased following the sacking of the widely-respected finance minister, Pravin Gordhan, in March.
But the ANC parliamentary party did not address these criticisms in a statement following the vote, which it called a "soft coup".
The statement also accused the opposition of attempting "to collapse government, deter service delivery and sow seeds of chaos in society to ultimately grab power".
However, the vote was not a rousing success for the governing party. The result means at least 26 ANC MPs rebelled, while another nine MPs abstained from voting.
In order for the no-confidence motion to pass, at least 50 out of the ANC's 249 MPs would have had to vote against the president.
The ANC's chief whip Jackson Mthembu said the party was planning to look into disciplining those who had voted against the president, South Africa's Times Live website reported.
But the rebels were praised by opposition leaders, who have repeatedly called for votes against the president.
The Democratic Alliance's Mmusi Maimane - who earlier said the vote was one between "right and wrong; between good and evil" - told reporters: "I applaud the courageous ANC people who moved across and said we will vote with our conscience and we will vote for change."
Julius Malema, leader of the Economic Freedom Fighters, said the vote had proved South Africa's democracy works - and warned Mr Zuma it proved they could unseat him.
Mr Zuma is due to step down as head of the ANC in December, ahead of the 2019 general election.
He has endorsed his ex-wife, Nkosazana Dlamini-Zuma as his successor.
Also vying for the leadership is Cyril Ramaphosa, a former trade unionist and one of South Africa's wealthiest politicians.
South African MPs will vote in secret on a motion of no-confidence in President Jacob Zuma on Tuesday, the parliament's speaker has announced.
Baleka Mbete made the ruling after opposition parties took the case to the Constitutional Court.
They believe that in a secret ballot, MPs from the governing African National Congress (ANC) would be more likely to vote against the president.
Mr Zuma has survived several previous votes of no-confidence.
The ANC has governed South Africa since the end of white-minority rule in 1994, and has a huge majority in parliament.
Ms Mbete's decision took many by surprise and injects a new element of uncertainty into the proceedings against the president, reports the BBC's Nomsa Maseko in Cape Town.
The question now is whether enough ANC MPs are prepared to make a stand against the president, she adds.
At least 50 out of the ANC's 249 MPs would need to vote against the president in order for the no-confidence motion to pass.
ANC MP Makhosi Khoza received death threats last month after she said she would vote against the president, and branded him "a disgrace".
Opposition Democratic Alliance leader Mmusi Maimane told journalists that now with the secret ballot, the ANC MPs "have no excuse".
In a statement, it added that the ANC will vote against the motion and not back the attempt to "collapse our democratically elected government".
The ANC has described the no-confidence motion as a "political ploy" designed to remove the government "outside of general elections".
This latest attempt to unseat Mr Zuma came after he fired his widely respected Finance Minister Pravin Gordhan and other ministers in a major cabinet reshuffle in March, sparking nationwide protests.
The president has also faced allegations of corruption and accusations that he has become too close to the wealthy Gupta family, who are accused of trying to influence political decisions, including the sacking of Mr Gordhan.
Mr Zuma and the Guptas have denied any wrongdoing.
Mr Zuma is due to step down as ANC leader in December. Several candidates are vying to succeed him as party leader, with the winner standing a strong chance of becoming South Africa's next president after elections in 2019.
The current favourites are deputy president Cyril Ramaphosa and Mr Zuma's former wife, and favoured candidate, Nkosazana Dlamini-Zuma.