The toll in one of Argentina's worst train accidents has risen to 49 while 600 others have been injured.
The casualties include 48 adults and a child; the train was carrying nearly 1,500 commuters at the time of the accident.
President Cristina Fernandez has declared two days of mourning and called off the Carnival festivities while expressing her condolences to the families of the victims.
Emergency workers are still pulling out the injured from the mangled chairs of the train by cutting open the roof of the chair to take out the trapped people.
Officials suspect a faulty brake system behind the cause of the accident, according to a Reuters report.
"The train entered Once station at 26 kilometers per hour (16 mph). We suppose there was some flaw in the brakes. The train folded up on itself," Reuters quoted Transport Secretary Juan Pablo Schiavi as telling the state news agency, Telam.
"The commuter train came in too fast and hit the barrier at the end of the platform at about 16 mph (26 kph), smashing the front of the engine and crunching the leading cars behind it; one car penetrated nearly 20 feet (six meters) into the next, " Schiavi added.
The accident has stirred up criticism about the overcrowded and disorderly rail system in Argentina which is run by the private companies with huge government subsidies.
Nearly ten million passengers commute every month on the Sarmiento line, which links Buenos Aires to its western suburbs.
The last major train accident in Argentina occurred in Feb 1, 1970, when a train smashed in to another killing nearly 230 people.