* Derailment caused by excessive speed - source
* Tragedy on eve of major religious festival
* One of Europe's worst rail disasters
By Teresa Medrano and Tracy Rucinski
SANTIAGO DE COMPOSTELA, Spain, July 25 (Reuters) - Thedriver of a Spanish train that derailed, killing at least 80people, was under police guard in hospital on Thursday after thedramatic accident which an official source said was caused byexcessive speed.
The eight-carriage train came off the tracks, hit a wall andcaught fire just outside the pilgrimage destination Santiago deCompostela in northwestern Spain on Wednesday night. It was oneof Europe's worst rail disasters.
The source had knowledge of the official investigation intoa crash which brought misery to Santiago on Thursday, the daywhen it should have celebrated one of Europe's biggest Christianfestivals. Authorities cancelled festivities as the city wentinto mourning.
The Galicia regional supreme court said in a statement thejudge investigating the accident had ordered police to take astatement from the driver.
He was being formally investigated and under police guardbut not under arrest, the court said. He was in hospital but itwas not clear what kind of injuries he had suffered.
Video footage from a security camera showed the train, with247 people on board, hurtling into a concrete wall at the sideof the track as carriages jack-knifed and the engine overturned.
One local official described the aftermath of the crash aslike a scene from hell, with bodies strewn next to the tracks.
The impact was so huge one carriage flew several metres intothe air and landed on the other side of a high concrete barrier.
Around 94 people were injured, 35 of them, including fourchildren, in a serious condition, the deputy head of theregional government said.
"We heard a massive noise and we went down the tracks. Ihelped get a few injured and bodies out of the train. I wentinto one of the cars but I'd rather not tell you what I sawthere," Ricardo Martinez, a 47-year old baker from Santiago deCompostela, told Reuters.
Newspaper accounts cited witnesses as saying the driver,Francisco Jose Garzon, who had helped rescue victims, shoutedinto a phone: "I've derailed! What do I do?".
The 52-year-old had been a train driver for 30 years, said aspokeswoman for Renfe, the state train company.
A court source told Reuters there was one driver on thetrain. Previously, a Galicia government source had said therewere two.
TRAIN HIT BEND AT SPEED
El Pais newspaper said the driver told the railway stationby radio after being trapped in his cabin that the train enteredthe bend at 190 kilometres per hour (120 mph). An officialsource said the speed limit on that stretch of twin track, laidin 2011, was 80 kph.
"We're only human! We're only human!" the driver told thestation, the newspaper said, citing sources close to theinvestigation. "I hope there are no dead, because this willweigh on my conscience."
Investigators were trying to find out why the train wasgoing so fast and why security devices to keep speed withinpermitted limits had not slowed the train.
Operated by state-owned company Renfe, the train was builtby Bombardier and Talgo and was around five years old. It hadalmost the maximum number of passengers.
Spain's rail safety record is better than the Europeanaverage, ranking 18th out of 27 countries in terms of railwaydeaths per kilometres travelled, the European Railway Agencysaid. There were 218 train accidents in Spain between 2008-2011,well below the EU average of 426 for the same period.
Firefighters called off a strike to help with the disaster,while hospital staff, many operating on reduced salaries becauseof spending cuts in recession-hit Spain, worked overtime to tendthe injured.
The disaster happened at 8.41 p.m. (1841 GMT) on the eve ofa festival dedicated to St. James, one of Jesus's 12 disciples,whose remains are said to rest in Santiago's centuries-oldcathedral.
The apostle's shrine is the destination of the famous ElCamino de Santiago pilgrimage across the Pyrenees, which hasbeen followed by Christians since the Middle Ages.
"The main mass (in the cathedral) was transformed from amass of joy into a mass of mourning," said Italian pilgrim IreneValsangiacomo.
KING, PM VISIT
One U.S. citizen died in the crash and five were injured,the State Department said in Washington. Mexico said one of itsnationals was among the dead.
At least one British citizen was injured, a British embassyspokesman said. People from several other countries werebelieved to be among the passengers.
People living nearby ran to the site to help emergencyworkers tend to the wounded. Ana Taboada, a 29-year-old hospitalworker, was one of the first on the scene.
"When the dust lifted I saw corpses. I didn't make it downto the track, because I was helping the passengers that werecoming up the embankment," she told Reuters. "I saw a man tryingto break a window with a stone to help those inside get out."
Prime Minister Mariano Rajoy, who was born in Santiago deCompostela, the capital of Galicia region, visited the site andthe main hospital on Thursday. He declared three days ofofficial national mourning for the victims of the disaster.
King Juan Carlos and Queen Sofia also went to Santiago andvisited the injured in hospital.
"All of Spain is united in grief with the bereaved families,"the king said.
Both Renfe and state-owned Adif, which is in charge of thetracks, opened an investigation into the derailment.
Passenger Ricardo Montesco told Cadena Ser radio station thetrain approached the curve at high speed, twisted and thecarriages piled up one on top of the other.
"A lot of people were squashed on the bottom. We tried tosqueeze out of the bottom of the wagons to get out and werealised the train was burning. ... I was in the second carriage and there was fire. ... I saw corpses," he said.
Clinics in Santiago de Compostela were overwhelmed withpeople flocking to give blood, while hotels organised free roomsfor relatives. Madrid sent forensic scientists and hospitalstaff to the scene on special flights.
Allianz Seguros, owned by Germany's Allianz, ownsthe insurance contract for loss suffered by Renfe passengers, acompany spokeswoman told Reuters. The contract does not coverRenfe's trains. The company had sent experts to the scene.
The disaster stirred memories of a train bombing in Madridin 2004, carried out by Islamist militants, that killed 191people, although officials do not suspect an attack this time.
Spain is struggling to emerge from a long-running recessionmarked by government-driven austerity to bring its deeplyindebted finances into order.
But Adif, the state railways infrastructure company, toldReuters no budget cuts had been implemented on maintenance ofthe line, which connects La Coruna, Santiago de Compostela andOurense and was inaugurated in 2011.
It said more than 100 million euros a year were being spenton track maintenance in Spain.