At least 34 people were killed when an underground train ran off the tracks and overturned at high speed in the eastern Spanish city of Valencia on Monday, officials said.
They said a wheel broke on a curve as the train approached the Jesus underground station and two train carriages derailed in the tunnel. More than 20 people were seriously injured.
Trapped passengers rang emergency services from mobile phones and 150 people were evacuated from the station platform. One middle-aged woman, her face blackened by what looked like soot, grimaced with pain as she staggered away from the station, her arm around a police officer. Officials ruled out a terror attack in a country still shaky from train bombings by militants that killed 191 people in Madrid in 2004.
"It seems this unfortunate accident was caused by excess speed and a wheel breaking just before it entered the station," government official Luis Felipe Martinez told Spanish radio, adding that the number of dead was still not confirmed.
Emergency services set up two field hospitals in tents on the street and a judge arrived to supervise the removal of bodies. Hospitals appealed for blood donors.
The accident took place days before Pope Benedict was due to visit Valencia for a 'World Meeting of Families' and pilgrims were already arriving in the Mediterranean seaside city.
CATASTROPHE: Thousands of yachting enthusiasts were also visiting Valencia, which is staging warm-up races for the Americas Cup.
A senior police officer at the scene said 34 people had been killed.
Police sealed off streets outside the station and crowds watched under bright blue skies as emergency crews rushed injured people into ranks of ambulances.
A 21-year-old student, Cesar Hernandez, said the train began travelling faster than usual and was shaking from side to side before the train braked suddenly and the carriages derailed.
Hernandez kicked the glass out of a door and walked out into the tunnel.
"There wasn't much light and I couldn't see much of what was on the tracks. I saw people on the ground, but I just ran," Hernandez told newspaper El Mundo, adding that he had declined emergency service offers of trauma counselling.
"I didn't want psychological help or anything. I just wanted to see my Dad," he said.
In September last year, three trains crashed into each other in Valencia's Metro system, injuring 16 people.
Monday's was the worst train accident in Spain since June 2003, when 19 people were killed when a passenger train travelling to Cartagena from Madrid crashed into the path of an oncoming goods train at Chinchilla.
The Pope has been informed of the accident and went to his private chapel to pray for the victims, state radio said.
The mayoress of Valencia Rita Barbera told reporters the accident was "a catastrophe, a tragedy".