Argentina train crash in Buenos Aires 'kills dozens'
The train hit the end of the platform at Once station in the capital Buenos Aires during the morning rush hour.
"We assume that there was some fault in the brakes," Transportation Secretary JP Schiavi said.
Dozens of people were trapped for hours in the wreckage but all have now been successfully taken to safety.
"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.
Police outside Once station had to "keep back the curious and concerned as paramedics treated the injured", eyewitness Tom English told the BBC.
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 added.