Firefighters worked frantically to pull people out of the wreckage and rush the injured to hospitals, officials said.
Police said they have confirmed the deaths of 11 victims. Officials said as many as 30 of the injured were very badly hurt, suggesting the death toll could climb substantially.
Argentina’s Transportation Secretary Juan Pablo Schiavi said most of the fatalities were among people who had been aboard the bus, including the driver.
The crash occurred at 7:00 am as thousands of commuters were pouring into the Flores district station in southwestern Buenos Aires on their way to work.
“A train entering Flores station hits a bus from the 92 Line, drags it and smashes it against the platform,” said Gustavo Gago, a spokesman for the Buenos Aires train operator.
“At that point, the train goes off the track, invading other tracks in its path and is struck laterally by a train that was entering Flores,” from another direction, he said.
Newspaper seller Lucas Sanz, 31, whose stand is 10 metres away, said he heard “a deafening noise and I saw the bus smashed into the train.”
“Terrified people began exiting the cars in all directions,” he said. “The police arrived quickly and began taking charge of the crowds that came in waves.”
Fire chief Omar Bravo said firefighters “rescued people who were in the bus, in the train and on the platform,” including a two-year-old toddler who was found under the platform.
Rescuers succeeded after two hours in freeing two people whose legs were trapped in the wreckage, one of whom was a conductor on one of the trains.
Authorities were investigating reports that the bus driver failed to heed a train crossing signal and breached the lowered barriers meant to signal that it is dangerous to cross the tracks.
“It was one of the saddest, most serious accidents in recent years,” said Mr Bravo.
In March 2008, 18 people were killed and 47 injured when a bus was hit by a train in Dolores, 212 kilometres south of Buenos Aires.
In February, a long distance train struck a suburban passenger train, leaving four dead and 120 injured.
Argentina’s deadliest train tragedy was in 1970, an accident that killed 200 people on Buenos Aires’ north end. –AFP