At least 19 children have been killed in a minibus crash near the South African capital, Pretoria, emergency services and officials say.
The children died after the vehicle burst into flames following a collision with a truck just north of the capital.
There were understood to be both primary and secondary school-aged children on board.
Panyaza Lesufi, the official responsible for education in Gauteng province, said it was a "dark day".
The minibus collided with a truck on the single carriageway R25, between Verena in Mpumalanga and Bronkhorstspruit in Gauteng, having left from Mahlenga High.
The emergency services rescued seven children before the bus burst into flames.
"It is believed the driver of minibus underestimated the speed of the truck and collided with him whilst turning," the Gauteng Education Department said in a statement.
Police later said the bus driver was also killed in the accident, while the driver of the truck survived.
Pictures show the minibus on its side, entirely burnt out.
In a statement, emergency medical service ER24 described arriving at the scene, where firefighters were tackling the flames. A number of children had already been pulled out by "members of the community", the statement said.
"Once the flames had been extinguished, paramedics found that approximately 13 children [were] lying trapped inside the vehicle. Unfortunately, nothing could be done for the children and they were declared dead on the scene," the statement added.
Time for change - by the BBC's Milton Nkosi in Johannesburg
There seems to be no end in sight to South Africa's road carnage.
This latest tragedy comes hot on the heels of a 50% increase of road deaths from last year's Easter period.
Authorities keep doing the same thing but expecting a different result.
In a country with one of the most advanced road networks on the African continent, clearly the problem lies elsewhere.
Drivers' behavioural patterns need to be changed through a combination of education and stricter law enforcement regime amongst other factors.
The transport minister once said "we cannot have a policeman at every intersection. We are not a police state".
Could that approach be the problem perhaps?
Hopefully this latest tragedy will shock South Africans, both in and outside government, into action which will ultimately bring an end to these unnecessary deaths.
The African National Congress (ANC) later said that it was "gravely saddened" by the deaths of the school pupils following the "heart-breaking accident" on Friday.
"It is a sad day for South Africa," the statement said, adding that the ANC "extends its deepest condolences to the bereaved families".
ER24 and the Gauteng Education Department had earlier reported that a total of 20 people had been killed, with the education department adding that two of the dead were adults.
"This is a huge loss and we're deeply pained by the tragic news," the education department tweeted.
South Africa has some of the deadliest roads in the world. According to the country's Road Traffic Management Corporation, there were 13,673 deaths in the 12 months from October 2015 - which equates to more than 37 people dying every day.