Police in South Africa said they have launched a manhunt for a convicted rapist who faked his own death in a daring prison break that has shocked the country.

Authorities believed Thabo Bester to have died after setting himself alight in a privately-run prison in Bloemfontein in May last year.

But at the weekend police said DNA tests revealed the charred remains found in the serial rapist's cell belonged to someone else.

"At this point our priority is to find this fugitive of justice and establish exactly how he faked his death," police spokeswoman Athlenda Mathe told AFP on Monday.

Dubbed the "Facebook rapist" Bester allegedly lured victims on the social media platform before raping and robbing them. At least one victim was killed.

In 2012 he was sentenced to life in prison for rape, robbery and murder.

On Sunday police said an autopsy revealed the body found in Bester's cell had died as a result of blunt force trauma to the head before it was set ablaze.

A fresh murder investigation has been opened.

The case has sparked outrage in South Africa, where women's rights groups have long accused the government of not doing enough to tackle violence against women.

"The unfolding of this story has been like a movie and sent shivers down everyone's spines...I can imagine what it did to the victims" Bafana Khumalo, the co-director of NGO Sonke Gender Justice, told AFP.

Between October and December last year police recorded more than 12,000 rapes across the country.

Doubts about Bester's death were first raised by local media outlet GroundUp last November.

Photographs purportedly showing the convict grocery shopping in an affluent Johannesburg suburb have since surfaced.

And some women have come forward alleging the convict made contact with them on social media.

Prior to his escape, Bester also reportedly ran a scam media business from inside prison using a false name.

A video of the criminal addressing a company event via video call from behind bars while pretending to be in New York has gone viral.

"The escape of Bester... is testament to the incompetence of the Correctional Services system, and the endemic corruption in the sector," Radical leftist opposition party, the Economic Freedom Fighters said in a statement.

Police have appealed to the public for any information relevant to the case.

"We want to find people who are directly involved in this matter as well as his accomplices," said Mathe.