It was scenes of horror and panic at the Once station on Wednesday morning when a packed commuter train crashed and came to a halt after slamming into a metal barrier in the station.

The force of the crash propelled the second train car nearly six metres into the first.

Passengers were thrown to the floor, many injured and blood-soaked by the shattered glasses and mangled metals.

"There was a terrible explosion and a brutal impact," Reuters quoted one of the passengers as saying.

Relatives and friends were seen wandering around the station to get information about their loved ones who were travelling on the train or waiting at the platform.

The death toll has reached 49 in the smash-up and more than 600 are believed to be injured. Officials are suspecting a faulty brake system behind the cause of the accident.

Take a look at the scenes of the accident at Once station in Buenos Aires: