Sadly there has been at least one fatality. A seven-year-old boy who had been trapped for over three hours has died. He was pronounced dead at the scene of the accident. The death toll is expected to increase.
Rescue services have been working hard. Initially around 100 people were trapped inside the carriages. Already seventy of these have been released and are receiving appropriate care. The strain on medical resources will also be high. The country's Transport Secretary Juan Pablo Schiavi issued a statment from the scene of the tragedy. In it he said, "the train was moving at a speed of 26 kilometres per hour when entering the station, however when it crashed, it had slowed down and was travelling at 20 kilometres per hour." "“the impact of the crash caused the second carriage to be pushed 6 metres into the first carriage of the train." Obviously the effect of the impact was to send passengers tumbling and hurtling forward.
The crash happened at 8.30am local time at Once station which is in the heart of Plaza Miserere, Buenos Aires.
Update 16.00GMT February 22, 2012: At least 40 [people are now known to have died as a result of this accident.
A subsequent update by the BBC, still on February 22, 2012, has the death toll at 49 and the injured at 600