JOHANNESBURG — Grace Mugabe, the wife of the president of Zimbabwe, appeared voluntarily at a police station in South Africa on Tuesday after she was accused of assaulting a young woman at an upscale Johannesburg hotel Sunday night, the South African police minister said.

Ms. Mugabe, 52, was not placed under arrest “because she cooperated and handed herself over,” Minister of Police Fikile Mbalula said in a video posted on the website eNCA, which added that she was scheduled to appear in court later on Tuesday.

Gabriella Engels, 20, has accused Ms. Mugabe of assaulting her while she was visiting Ms. Mugabe’s sons in a hotel room, and has said that Ms. Mugabe’s bodyguards stood by and watched.

Ms. Engels posted several photos on social media showing a gash in her forehead that she said was caused by Ms. Mugabe. “I had no clue who this woman was when she started beating me,” Ms. Engels told a local radio station, 702.