At least 300 people, including many schoolchildren, have been injured after two passenger trains collided near the South African capital, Pretoria, officials say. Medical workers say 28 people were seriously hurt.
The theft of cables used for signalling, compounded by human error, caused the crash, said the head of South Africa's rail authority.
The early morning accident happened when a train crashed into a stationary train near Attridgeville, a township west of Pretoria.
"Many are walking wounded and already left. There are 20 people in serious condition and one, the driver of the second train, is in a critical condition," local emergency services spokesman Johan Pieterse said.
"Both of the trains were full of commuters and between them were lots of schoolchildren on the way to school," the spokesman said.
A helicopter has airlifted one of the train drivers to a nearby hospital after he was trapped in the wreckage for two hours.
A spokesman for the local emergency services told the BBC it had transported more than 200 people, three of whom were critical, while 19 had serious injuries. The private Netcare 911 service said it had assisted 100 people, with three critical and three more seriously injured. The injured have all been taken to hospitals in Pretoria and Johannesburg.
Rescue workers struggled to cut away the tangled wreckage of the trains to free the passengers.
One of the train drivers was freed from the carriage where he was trapped for two hours. He was among those critically injured.
The trains were on the same line toward the capital Pretoria when one train hit the other from behind.
The trains were operated by Metrorail, the country's rail system in cities.
It is just the latest serious rail accident to hit South Africa's urban rail network. In 2011, 857 commuters were injured in Johannesburg's Soweto township when a passenger train smashed into a stationary train during the peak rush hour period.
The Passenger Rail Agency of South, has itself described its passengers as "travelling like cattle."
Over 90 percent of commuter trains in South Africa date back to more than fifty years, the most recent dating from 1986.