A train crash at a station in the Argentine capital, Buenos Aires, has killed 49 people with hundreds more injured, police say.
The train slammed into the barrier at the end of the platform at the Once station during the morning rush hour.
"We assume that there was some fault in the brakes", Transportation Secretary JP Schiavi said.
Eyewitnesses said the train was travelling fast. Dozens of people remain trapped.
"The train was full and the impact was tremendous," a passenger identified as Ezequiel told local television.
Medics at the scene were overwhelmed by the casualties, he added.
"People started to break windows and get out however they could," another eyewitness told Reuters.
"Then I saw the engine destroyed and the train driver trapped amongst the steel. There were a lot of people hurt, a lot of kids, elderly," the eyewitness added.
The train had hit the barrier at about 12mph (20km/h), destroying the front of the engine and crunching the carriages behind it, Mr Schiavi said.
One of the carriages was driven nearly 6m (20ft) into the next, he said.
Emergency workers are working to extract dozens of people trapped inside the first car, said health official Alberto Crescenti.
Survivors told local media that many people had been injured in a jumble of metal and glass.
Some suffered fractures and other serious injuries.
The accident is Argentina's worst train crash since 1970.
In September 2011, 11 people died when a commuter train in Buenos Aires hit a bus crossing the tracks and then hit a second train coming into a station.