BUENOS AIRES--A packed commuter train crashed at a Buenos Aires station during Wednesday's morning rush hour, killing 49 people and injuring more than 600 in Argentina's worst rail disaster in three decades.

Passengers said the force of the collision propelled the second train car inside the first carriage, trapping dozens of people in the wreckage alongside the busy platforms at Once station. Officials said faulty brakes were suspected of causing the accident and witnesses said the train hurtled into the buffers.

"I said, 'Be careful, the train isn't braking' ... I moved backward because I thought it was going to run me over," said Alfredo Velazquez, 33, a shopping center manager who was waiting on the platform. "There was a terrible explosion and a brutal impact," he said.

Commuters inside the train "flew through the air," a passenger wearing a neckbrace who identified himself as Fabio told local television. "There were lots of people thrown to the floor, injured, bloodied."

"The train (car) was embedded inside the other ... the seats were gone, they disappeared, and people were jumping out of the window," he said. A police captain said 49 people were killed, including one child.

Relatives and friends wandered around the train station later in the day, trying to find news of missing loved ones. President Cristina Fernandez expressed her "profound sadness," calling off Carnival festivities and declaring two days of mourning.

Most of the victims were traveling in the first two cars of the eight-car train, which Transport Secretary Juan Pablo Schiavi said was carrying between 1,200 and 1,500 passengers. "The train entered Once station at 26 kilometers per hour (16 mph) ... we suppose there was some flaw in the brakes," he was quoted as saying by state news agency Telam. "The train folded up on itself."

The 28-year-old driver remained in intensive care and about 460 of the injured were still being treated in local hospitals.

Wednesday's crash is bound to fuel criticism of the country's dilapidated and overcrowded rail services, which are run by private companies with hefty state subsidies and are prone to accidents and delays. Argentina's once-extensive rail network was largely dismantled during privatizations in the 1990s.