JOHANNESBURG (AP) — Emergency responders say at least 20 children have been killed when their minibus collided with a truck northeast of South Africa's capital.

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

ER24 says responders found about 13 children trapped inside the vehicle after its flames were put out. The other children were found outside the minibus.

The emergency service says the cause of the crash is not yet known. It occurred between the communities of Verena and Bronkhorstpruit.