Images from the scene show the 22-seat bus flipped on to its side, still smoking after it caught fire following the collision.
It seems to have collided with a large construction truck, which also burst into flames from the impact and has suffered extensive damage.
The condition of the driver of the truck is unknown.
The children were killed in a car crash on Friday
Emergency services confirmed the children were killed when the minibus burst into flames following the horrific collision.
Many of the children were thought to be trapped in the bus after it crashed in Mpumalanga province, north of the city of Pretoria, in the north-east of the country.
They were understood to be both primary and secondary school age children on board.
Russel Meiring, ER24 spokesman said: "The number now is at least 17 fatalities."
The bus burst into flames following the collision
About 20 children were in the minibus when it collided with the truck, he said.
Gauteng province's education minister has described it as a "dark day".
The cause of the accident is not yet known, but local authorities are on scene for further investigations.
No further information is available at this time.
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