Two passenger trains packed with school kids and rush-hour commuters collided near the South Africa capital Pretoria on Thursday, injuring up to 300 people, medics said.
The accident took place before 8am when a commuter train heading from the suburbs to the capital ploughed into a stationary train on the same track.
Medical workers said that up to 300 people had been treated for various degrees of injury.
"We do have 20 seriously injured," said Johan Pieterse of Tshwane Emergency Services.
"Both of the trains were full of commuters and between them were lots of school children on the way to school," said Pieterse.
"We counted about 50-plus children," he added.
At least three people were said to be in a "critical" condition according to Chris Botha, a spokesperson for emergency services provider Netcare 911.
"The people who were critically injured suffered multiple injuries to the body," said Botha.
At least one person was airlifted to the nearby Milpark Hospital, others were taken by ambulance and many were treated at the scene.
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's critical at this stage," said Pieterse.
The trains were operated by Metrorail, the country's rail system in cities.
The cause of the accident is unknown.
"At this stage we do not want to speculate," said Metrorail spokesperson Lillian Mofokeng.
It was 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.
The network is currently undergoing a major revamp to upgrade its fleet, spending R123-billion over 20 years.