WARNING: Video contains footage that some may find disturbing
Spanish media have named one of the drivers being formally investigated by police as Francisco Jose Garzon Amo.
Earlier in the same day, distressing video footage emerged of the moment a train in the Santiago de Compostela crashed, killing up to 80 passengers and leaving up to 168 injured in one of the worst train crashes in four decades.
36 of the injured, including four children, remain in a critical condition.
The footage, recorded by a security camera positioned above the track, shows the trains first carriage behind the locomotive come off the tracks first, slamming the tail of the locomotive into a concrete wall.
All the carriages can then be seen veering off the tracks as the locomotive hurtles towards the camera.
One of the train drivers is now being formally investigated by police, according to the BBC.
Spanish national newspaper El Pais has reported that the train operator admitted he had been driving the train at 180 km/h immediately after the incident.
The train, which was heading from Madrid to Ferrol, crashed off the high speed section of tracks near Santiago de Compostela in Galicia. After emerging from a tunnel the train, which was travelling at a "very fast" speed, it derailed on the curve and sent at least six carriages flying off the tracks at 8.41pm local time on Wednesday.
At least one caught fire in a scene that Alberto Nunez Feijoo, President of the region of Galicia described as “Dante-esque”.
Renfe, the state-owned train operator said in a statement that 218 passengers and an unspecified number of staff were on board at the time of the accident.
More than 70 bodies have been reportedly removed from the wreckage and rescuers are still searching through the smouldering carriages in search of survivors. A British national is among the injured, the Foreign Office has confirmed
Three days of mourning have now been declared in the Galicia region.
Foreign Secretary William Hague said the British Embassy were working to with Spanish authorities to help respond to the tragedy. “I was very saddened to hear of the terrible train accident near Santiago de Compostela in Spain last night," he said.
”My thoughts are with all those affected and their friends and family. The British Embassy team in Spain are working closely with the Spanish authorities as they respond to this tragedy.
“We know that one British citizen was injured in this accident and the embassy has been providing consular support.”
A photographer at the scene said he witnessed dozens of dead bodies being extracted from the wreck by emergency workers. TVE showed footage of what appeared to be several bodies covered by blankets alongside the tracks next to the damaged train wagons and rescue workers entering toppled carriages through broken windows. Rescue workers were also seen in the television images caring for people still inside some of the wagons.
Television footage showed one wagon pointing upwards into the air with one of its ends twisted and disfigured. Another carriage had been severed in two and could be seen lying on a road near to the track.
The train, which is owned by Renfe, was not an AVE high speed train and was instead a relatively luxurious version that uses the same track as Spain's fastest expresses.
It was the country's deadliest train accident in decades. In 1944, a train travelling from Madrid to Galicia crashed and killed 78 people. Another accident in 1972 left 77 dead on a track to south-western Seville, according to Spanish news agency Europa Press.
King Juan Carlos and Prime Minister Mariano Rajoy, a native of Galicia, both offered their condolences. Mr Rajoy arrived on scene at 10:45am on Thursday morning.
The incident happened as Catholic pilgrims converged on Santiago de Compostela to celebrate a festival honouring St James, the disciple of Jesus whose remains are said to rest in a shrine. The city is the main gathering point for the faithful who make it to the end of the El Camino de Santiago pilgrimage route that has drawn Christians since the Middle Ages.
Officials said they believed the crash was an accident but declined to offer more details, saying an investigation was under way into the cause. Renfe said that it and track operator Adif were collaborating with a judge appointed to investigate the accident.
Feast day festivities planned in Santiago de Compostela were cancelled, town hall spokeswoman Maria Pardo told TVE.
The train involved was a bi-mode train capable of running on electrified high-speed lines as well as operating independently on non-electrified tracks.
Peter Sheppard, from the UK's Institution of Engineering and Technology, said: "Railways generally have a very high safety record, but it is disappointing to see two recent major incidents (France and Spain) where there has been a significant loss of life.
"However - and this is based on news reports only - it would seem that both are as a result of human error and not the technology involved. "
He went on: "The former case (France) appears to be a maintenance issue, the latter case (Spain), based on the first reports, seems to be as a result of a significant over-speed (although there could well be other factors as what is perceived by passengers is sometimes different to reality).
"What has to happen when the inquiries are complete is to determine if there is any methods by which technology could have intervened, prevented or given early warning of these accidents and either supported the infrastructure maintenance teams or advised/intervened in the cab."