A minibus crashed and burned on Friday killing at least 20 children in a horrific traffic accident outside the South African capital Pretoria.

Paramedics treated the injured at the scene after the van carrying students collided with a transport truck northeast of the capital, about 70km from Pretoria.

"It is confirmed 20 children have been killed," Russel Meiring, spokesman for the ER24 emergency medical service, told AFP news agency.

"Paramedics arrived on the scene to find the fire services already in attendance. The fire services had already extinguished the burning vehicle, which was found lying on its side."

The victims were between five and 10 years old, said Meiring. He said several children survived after being pulled from the wreckage near Bronkhorstspruit, east of the capital.

Authorities were investigating the cause of the crash. "We are trying to find out exactly what happened," he said.

Children trapped

Many children were trapped inside the vehicle and most of the fatalities were declared dead at the site of the accident. Department of education spokesman Steve Mabona said some of the bodies of the children were charred beyond recognition.

Images posted by the ER24 medical service on Twitter showed the minibus smoking and twisted on its side next to the truck.

"The children were treated for their injuries and provided with advanced life support interventions before they were transported to various hospitals in the area for further treatment," ER24 said.

Despite sophisticated road networks, South Africa battles with a high rate of road fatalities blamed mostly on speeding, reckless driving, unroadworthy vehicles and failure to use seat belts.

A total of 235 people died in accidents on South Africa's roads during the recent Easter period, a 51 percent increase over the same period last year, according to the country's Road Traffic Management Corporation.