South African police were caught on video dragging a man hundreds of meters from the back of a pick-up truck, hours before he died in custody, drawing a storm of protest against a force accused of routine brutality.

The 27-year-old Mozambican taxi driver, Mido Macia, was found dead in detention with signs of head injuries and internal bleeding, according to an initial postmortem report released by the country's police watchdog.

The incident, videotaped on Tuesday and broadcast nationwide on Thursday, was condemned by President Jacob Zuma and opposition politicians.

"The visuals of the incident are horrific, disturbing and unacceptable. No human being should be treated in that manner," said Zuma in a statement that described the incident as "the tragic death of a man in the hands of the police.”

Police told media they detained Macia after he parked illegally, creating a traffic jam, and then resisted arrest.

The video clearly shows the man scuffling with police, who subdue him. He is then bound to the back of the pick-up by his arms before the vehicle drives off in front of scores of witnesses in the east Johannesburg area of Daveyton.

Police commissioner Riah Phiyega said she was looking into the "alleged brutal treatment" by officers "in a very serious light and it is strongly condemned.”

Scandals

Her force has been caught up in a series of scandals in recent months.

The lead detective in the murder case against Olympic and Paralympic star Oscar Pistorius was removed from the investigation last week when it emerged he was facing seven attempted murder charges for allegedly opening fire on a minibus full of passengers.

Police shot dead 34 striking workers at a platinum mine in August last year — the deadliest security incident since apartheid ended in 1994.

The video footage and the man's death raised fresh concerns about police brutality in a country where more than 1,200 people a year die while in custody.

The incident dominated the agenda on talk shows and social media through the day.

"How much longer must South Africans live in fear of the very people who are supposed to protect them?" the opposition Democratic Alliance said in a statement.

The government's police watchdog investigated 1,276 cases of people dying in police custody in 2011. There were 30 police convicted of criminal acts for killing those in custody during the period, it said.

Zuma's African National Congress, which took power when apartheid ended, has tried to change a police force known for the arbitrary and brutal killings of thousands who wanted to end white-minority rule.

The ANC government changed the name from police "force" to police "service" and said its focus was to protect all citizens.

But the police service today is filled with underpaid officers who have done little to combat some of the highest crime rates of any of the Group of 20 global economic powers.