"He found his friend on top of his aunt and had a fight with him."

Gauteng community safety MEC Faith Mazibuko expressed shock on Tuesday at the rape of a mentally ill Soweto woman.

"No stone will be left unturned in the criminal justice system to bring the perpetrator to book," she said in a statement.

The 47-year-old woman was raped, allegedly by her nephew's friend, in Zola on Saturday night.

Police said the alleged rapist and the nephew were at a shebeen on Saturday night. The man left.

The nephew, knowing his friend was going to his aunt's house in Zola, left the shebeen shortly afterwards, Warrant Officer Kay Makhubela said.

"He found his friend on top of his aunt and had a fight with him."

The man ran away and was still at large.

"We need to stand together as communities and continue to fight against this scourge of people who prey on the vulnerable," Mazibuko said.

She said her department was providing medical and legal assistance and counselling for the victim through Ikhaya Lethemba, a centre for abused women and children.