At least 11 people have died in Argentina after a train slammed into a bus crossing the tracks and then hit a second train coming into a station, accoding to the BBC.
More than 200 people were injured, some seriously, a police spokesman said.
The crash happened during the morning rush hour as hundreds of commuters were waiting at the station in Flores, a Buenos Aires suburb.
Officials are investigating reports the bus driver, who is among the dead, failed to heed a stop signal.
Fire chief Omar Bravo said the collision was "one of the worst and saddest accidents of recent years" in Argentina.
Many rail lines go through residential areas of Buenos Aires, and it is not unusual to see drivers or pedestrians ignoring the warning signs of an oncoming train, says the BBC`s Vladimir Hernandez in Buenos Aires.
The accident happened at about 06:00 local time (09:00 GMT) on the Sarmiento line, which connects the centre of Buenos Aires with the western suburbs.
The impact smashed the bus into the train station where it was crushed against a platform by the locomotive.
The front of the train was derailed and hit another train that was leaving the station in the opposite direction.
Transport Secretary Juan Pablo Schiavi said most of the fatalities had been on board the bus. He also said children were among the injured as many parents use public transport to take them to school.
Mr Bravo said those rescued included a two-year-old child who was found under the platform.
Nine people died at the scene and two others in hospital, officials said. About 20 of the injured are said to be in a critical condition.
Officials are investigating reports that the bus driver did not stop and went through lowered barriers in an attempt to cross the railway line.
Train company spokesman Gustavo Gago said it believed the bus had "crossed on to the level-crossing when the barriers were low, but we await the results of the investigation to see if this is what happened".
A total of 100 ambulances and 10 fire engines were sent to the scene. Some of the injured were taken to local hospitals, some by helicopter.
According to the Argentine newspaper Clarin, firefighters took two hours to remove one of the train drivers who was trapped in the wreckage.