A video of a 27-year-old Mozambican taxi driver being dragged to his death handcuffed to the back of a South African police van for 400 metres has gone viral.
South Africa's police watchdog said it had opened an investigation into the death of Mido Macia, who was arrested in the eastern Johannesburg suburb of Daveyton.
"We are investigating an incident involving the death of a man, allegedly at the hands of the police. We are shocked by the footage which has been released," Independent Police Investigative Directorate spokesman Moses Dlamini said.
Macia reportedly got into a heated altercation with officers who had accused him of parking on the wrong side of the road.
They arrested him but he resisted being forced into the back of the police van. After a prolonged scuffle involving a number of officers and Macia, footage taken at the scene shows him tied to the back of the vehicle which is then driven off.
Macia was taken to a local police station where was beaten up, according South Africa's Daily Sun newspaper, which first posted the video online.
"[They] took him to the cop shop where, say other inmates, they beat him to death," one prisoner told the newspaper.
The body of a 27-year-old man, identified as Macia, was found in a cell by another policeman a few hours after the arrest.
According to a post mortem examination he had died of head injuries and internal bleeding.
"As horrific as it is, it is not exceptional. Hardly a week goes by without such stories of brutality," said Jacob van Garderen, national director of Lawyers for Human Rights.
"They are there for safety, but we as a people fear them more," said Johannesburg resident Alfonso Adams of the police. "You don't know who to trust any more."
At least four policemen are depicted in the video taking part in the brutality. Authorities have declined to say if any officers have been suspended.
Dlamini said: "We can only investigate and recommend suspension. We have no power to say that they should be removed from their jobs."