* One of Europe's worst rail disasters
* Train derailed on eve of ancient city's main festival
* Government working on hypothesis it was an accident
By Miguel Vidal
SANTIAGO DE COMPOSTELA, Spain, July 24 (Reuters) - At least 45 people were killed and 70 injured when a train derailed on the outskirts of the northern Spanish city of Santiago de Compostela on Wednesday in one of Europe's worst rail disasters.
Bodies covered in blankets lay next to the overturned carriages as smoke billowed from the wreckage. Firemen clambered over the twisted metal trying to get survivors out of the windows.
The government said it was working on the hypothesis the derailment was an accident - though the scene will stir memories of 2004's Madrid train bombing, carried out by Islamists, that killed 191 people.
The train operated by state rail company Renfe with 247 people on board derailed on the eve of the ancient city's main festival when thousands of Christian pilgrims travel in to pack the streets.
"It was going so quickly ... It seems that on a curve the train started to twist, and the wagons piled up one on top of the other," passenger Ricardo Montesco told Cadena Ser radio station.
"A lot of people were squashed on the bottom. We tried to squeeze out of the bottom of the wagons to get out and we realised the train was burning ... I was in the second wagon and there was fire ... I saw corpses," he added.
One witness near the scene told the radio station she heard an explosion before seeing the derailed train.
Prime Minister Mariano Rajoy, who was born in Santiago de Compostela, held an emergency meeting with his ministers. He would visit the site on Thursday morning, his spokeswoman added.
The head of the surrounding Galicia region, Alberto Nunez Feijoo, said at least 45 people were killed and round 70 injured, more than 20 of them seriously.
"The scene is shocking, it's Dante-esque," he said in a radio interview.
The train was travelling from Madrid to Ferrol on the Galician coast when it derailed, state train company Renfe said in a statement.
The crash happened a day before the city's main festival focused on St James, one of Jesus's 12 disciples whose remains are said to rest in the city.
The apostle's shrine there is the destination of the famous El Camino de Santiago pilgrimage, followed by Christians since the Middle Ages.
The derailment happened less than two weeks after six people died when a train came off the tracks and hit the platform at a station in central France.
That accident may have been caused by a loose steel plate at a junction, French train operator SNCF said.
It was one of the worst rail accidents in Europe over the past 25 years.
In November 2000, 155 people were killed when a fire in a tunnel engulfed a funicular train packed with skiers in Austria.
In Montenegro, up to 46 people were killed and nearly 200 injured in 2006 when a packed train derailed and plunged into a ravine outside the capital Podgorica.
In Spain itself, 41 people were killed the same year when an underground train derailed and overturned in a tunnel just before entering the Jesus metro station in Valencia.