A man who who saved a 13-year-old girl from being raped said he was not a hero because "it's what any ordinary person would do".

Bernard Erasmus, 30, of Somerset West, said he had not stopped to think about what he was doing. Erasmus was so determined that he managed to wrestle the attacker's knife away from him.

The suspect was later arrested and charged with rape.

Police have hailed Erasmus as a hero for taking action when he saw a crime being committed. But they also warned that citizens who intervened to prevent a crime should be certain that they could do so without risking their own lives and without breaking the law.

Erasmus said he had left work on Saturday at 10am. While driving along a farm road surrounded by long grass near Somerset West, he had seen a man and a girl fighting.

"The girl's clothes were ripped off her body. She was making a lot of noise. She was screaming and trying to hit the man on top of her," Erasmus said.

He had stopped his car and gone to help the girl. He said the suspect had seen him and started running.

Without thinking, Erasmus had given chase.

He caught up with the suspect, who had allegedly pulled out a knife. The two became involved in a scuffle, but Erasmus had been able to get the knife away from the man.

The suspect had then run away.

By the time Erasmus returned to the girl, "she was in a terrible state".

The two had then gone to the police station to lay charges and give statements.

The 22-year-old man was arrested on Sunday, and appeared in the Somerset West Magistrates' Court yesterday morning. He is due to appear again next week.

Erasmus said he did not consider himself a hero. "That's what any ordinary person would do. It was my duty to help my fellow person," he said.

He said he was concerned that criminals were operating in a "comfort zone".

"They don't even wait for it to be dark; they do these things in broad daylight," said Erasmus.

The suspect had been accused of rape on two previous occasions, but the cases had been thrown out when the alleged victims - both minors - failed to arrive at court to testify.

Today police spokesman Andre Traut commended Erasmus for his actions, but warned that members of the public should be certain that they were able to act.

"The police encourage public in-volvement in the prevention or suppression of crime, but we want people to be sure they are capable of doing it and that they should not risk their own lives," he said.

"People should make sure they know what the Criminal Procedures Act requires with regard to their action. If he (Erasumus) had a firearm, for example, he could have used it only in a situation where his own or somebody else's life was clearly in danger. In a case of rape, this is most likely the case.

"But you cannot use a firearm to protect property, a wallet or a cell phone, for example. The violence you use to stop a crime must be in line with the violence used in the perpetration of the crime."

Additional reporting by Henri du Plessis