At least 49 people were killed and 600 more injured after a commuter train was derailed at a station during the morning rush-hour in Buenos Aires.

Some three hours after the crash, rescuers were still working to free trapped passengers from the wreckage of the front carriages. The cries of survivors could be heard from within the twisted metal as emergency services struggled to cut them free.

Authorities confirmed that there were 49 deaths, among them a child, but warned that the number was likely to rise. Some 600 passengers were also injured with several hundred being treated at hospitals in the capital. Dozens were said to be in a serious condition.

Survivors of Argentina's worst rail accident in more than three decades described how the overcrowded train had failed to stop as it entered the Once railway terminus in the west of the city.

The cause of the accident has yet to be established. Some reports said the train's brakes may have failed, causing it to smash into the barrier at the end of the line. Others speculated that it had been travelling too fast when it entered the station.

Juan Pablo Schiavi, Argentina's transport minister visited the scene and said the first carriage was the worst affected. It had become crushed between the engine and the next carriage, "which penetrated nearly 20 feet into it", he said.

"There are people trapped alive in the wagons, some with complex cases of chest trauma," the minister said. "The accident is very serious. There are carriages on top of carriages." With more than 800 passengers on the train when it crashed into the buffers just after 8.30am yesterday (Wednesday), the aisles were cramped with people standing between the seats.

Many where thrown forward by the force of the crash. Others received abrasions and other injuries as glass from the windows smashed with the crumpling of the carriages.

"The train was full and the impact was tremendous," a passenger identified as Ezequiel, who said he had been travelling in the first carriage, told local television.

"There are people with broken bones and losing a lot of blood. There are a lot of injuries. People were panicking, desperate to get out."

The driver survived the crash and was taken to hospital but doctors said it was too early to attempt to talk to him in the hope of shedding light on the cause of the crash. A representative from the transport union said that the engine had been checked the day before and that there was no suggestion of faulty brakes.

Ruben Sobrero, union chief on the Sarmiento line, told Radio La Red: "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."

It is the third train crash in Buenos Aires in just over six months. Seventeen people were injured when two passenger trains collided in December.

Last September, nine people died and 212 were injured when two trains and a bus crashed at a level crossing in Buenos Aires.

The worst accidents in Argentine history include a crash in 1970 that killed more than 230 people and another in 1978, in which 55 died.