Wednesday, killing several people and injuring hundreds of morning commuters, authorities said.
"There are fatalities," said Alberto Crescenti, the city's emergency medical director. He declined to say how many, but when asked about reports that as many as 40 had died, he replied, "It's possible."
Forty deaths would be the highest death toll from a train accident since Feb. 1, 1970, when a train smashed into another at full speed in suburban Buenos Aires, killing 200 people.
Crescenti said at least 550 people were injured, and said that 30 people remain trapped inside the first car, where rescuers carved open the roof and set up a pulley system to extract them.
The commuter train came in too fast and hit the barrier at the end of the platform at about 12 mph (20 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, Argentina's transportation secretary, J.P. Schiavi told reporters at the station.
Most damaged was the first car, where passengers make space for bicycles. Survivors told the TeleNoticias channel that many people were injured in a jumble of metal and glass.
There have been five serious train accidents since Dec. 2010; the most deadly of these happened last Sept. 13, when a bus driver crossed the tracks in front of an oncoming train, killing 11.
"This machine left the shop yesterday and the brakes worked well. From what we know, it braked without problems at previous stations. At this point I don't want to speculate about the causes," Ruben Sobrero, union chief on the Sarmiento line, told Radio La Red.
