At least 49 people have been killed and more than 600 injured in the worst train crash in Argentina in 40 years, officials say.

阿根廷发生40年以来最严重的一次列车碰撞事故，至少49人死亡、600人受伤。

The train hit the end of the platform at Once station in the capital Buenos Aires during the morning rush hour.

"We assume that there was some fault in the brakes," Transportation Secretary JP Schiavi said.

Dozens of people were trapped for hours in the wreckage¹ but all have now been successfully taken to safety.

The government declared two days of mourning and called off planned carnival²（狂欢节） festivities in the country.

Jumble³ of metal

"The train was full and the impact was tremendous," a passenger identified as Ezequiel told local television after the crash on Wednesday.

Medics at the scene were overwhelmed by the casualties, he added.

"People started to break windows and get out however they could," another eyewitness⁴ told Reuters.

"Then I saw the engine destroyed and the train driver trapped amongst the steel. There were a lot of people hurt, a lot of kids, elderly," the eyewitness added.

Police outside Once station had to "keep back the curious and concerned as paramedics（护理人员） treated the injured", eyewitness Tom English told the BBC.

The train had hit the barrier at about 12mph (20km/h), destroying the front of the engine and crunching⁵ the carriages behind it, Mr Schiavi said.

One of the carriages was driven nearly 6m (20ft) into the next, he added.

Survivors⁶ told local media that many people had been injured in a jumble（混乱） of metal and glass.

Emergency medical system director Alberto Crescenti said that some passengers who survived had to have limbs amputated（截肢） . Many suffered from arrested breathing and trauma⁷ to the thorax（胸膛） region.

Many are in a critical condition in the city's hospitals and there are concerns that the death toll⁸ could rise, the BBC's Vladimir Hernandez in Buenos Aires reports.

Five accidents have occurred in and around the city in recent months, our correspondent says.

Many parts of Argentina's rail network are antiquated⁹ and in need of repair and this incident will increase concern about lack of investment in the system, he adds.