At least 49 people were killed on Wednesday when a packed commuter train slammed into a retaining wall at a railway terminus here during rush hour, a police spokesman said.
"Unfortunately, we must report that there are 49 dead in the accident," police spokesman Nestor Rodriguez told a news conference.
At least 550 people were injured in the crash, which witnesses said occurred after the train's breaks failed as it was arriving at a station on the western outskirts of Buenos Aires.
Transportation Secretary Juan Pablo Schiavi gave the toll and said many of the passengers were badly injured, including some with multiple fractures and abrasions, adding that 'there could be fatalities' among the casualties.
He added that there were an unknown number of commuters still trapped in the wreckage of the train.
"The train was full and the impact was tremendous," a passenger identified only as Ezequiel told local television, stating that medics at the scene were overwhelmed.
Local television pictures showed a trapped train driver and several people being carried away from the scene on stretchers.
The accident occurred just five months after another major transit incident rocked the Argentine capital, during a morning rush hour crash involving two trains and a bus.
That accident in September killed 11 people including the bus driver and injured more 200.
The region's transit system has been plagued with serious accidents in recent years.
In March 2008, 18 people were killed and 47 injured when a bus was hit by a train in Dolores, 212 kilometers (132 miles) south of Buenos Aires.
Argentina's deadliest train tragedy was in 1970, an accident that killed 200 people in northern Buenos Aires.
