South African police say Zimbabwe's first lady will be charged with assault after she allegedly attacked a model at a hotel in Johannesburg.

Grace Mugabe, wife of President Robert Mugabe, addresses a rally of the ruling ZANU (PF) in Chinhoyi, Zimbabwe July 29, 2017.
Grace Mugabe, wife of President Robert Mugabe, addresses a rally of the ruling ZANU (PF) in Chinhoyi, Zimbabwe July 29, 2017. (Reuters)

The wife of Zimbabwe's president has been accused of assaulting a young woman at an upscale Johannesburg hotel.

It was not immediately clear where Grace Mugabe was. Minister of Police Fikile Mbalula said in a video posted by local broadcaster eNCA that she had handed herself over to police.

But a police spokesman, Vishnu Naidoo, later said no arrest had been made and police were talking with the suspect's lawyers. He would not name the suspect, saying she had not yet appeared in court.

"There was a criminal case opened in Sandton at Morningside (station) yesterday, but I can not release any name. Right now we have not arrested anybody," Naidoo said.

The case draws yet more attention to the increasingly outspoken wife of the world's oldest head of state, 93-year-old President Robert Mugabe. 

Twenty-year-old model Gabriella Engels has accused Grace Mugabe of assaulting her on Sunday night while she was visiting Mugabe's sons in a hotel room in an upscale Johannesburg suburb. 

She claims the first lady's bodyguards stood by and watched as Mugabe attacked her.

Engels posted several photos on social media showing a gash in her forehead, which she called a result of the alleged encounter.

"She flipped and just kept beating me with the plug. Over and over," Engels told local news channel News24. "I had no idea what was going on. I was surprised . I needed to crawl out of the room before I could run away."

Engels told local radio station 702 that "I had no clue who this woman was when she started beating me."

Mugabe, who is 41 years younger than her husband Robert, has two sons and one daughter with the Zimbabwean president.

Sizakele Nkosi-Malobane, a provincial minister in Gauteng province, told Jacaranda FM that the case should be pursued through the courts.

"We hope that it will send a strong message to all leaders who abuse their power and assault innocent people in our country," she said.

Grace Mugabe regularly speaks at rallies in Zimbabwe and is seen as one potential successor to take over from her increasingly frail husband.

Last month she urged her 93-year-old husband to name his chosen successor, fuelling renewed speculation about the race to take over from the world's oldest national leader.

The Zimbabwe government made no immediate comment.