At least 30 people have been killed in a subway train derailment in the eastern Spanish city of Valencia, officials say.
Spanish newspaper El Pais put the death toll at 34, and said 14 people were seriously injured, including a pregnant woman.
The accident happened at 1 p.m. (7 a.m. ET) between two downtown stations -- Jesus and Plaza de Espana -- CNN's sister network CNN+ reported.
Valencia journalist Miguel Olavares told CNN that authorities were investigating three possible causes of the tragedy.
First that a tunnel ceiling had collapsed, bringing the train off the rails. The second possibility was that it had problems with the wheels on one side, he said. The third was that the train had been speeding.
Olavares said that the city's subway system had opened in 1998 and had suffered only one previous minor accident.
Journalist Enrique Pallas, speaking from the scene, said that "90 percent" of the dead and injured had been inside the train.
The train was traveling along the Number 1 line when it derailed in the subway tunnel along a curve in the track -- called a precaution zone -- between the two stations, said CNN+.
A passenger using his cellphone first reported the accident.
Vicente Rambla, representative of the Regional Government of Valencia, said the incident did not appear to be related to terrorism.
About 150 people were evacuated from the tunnel after the train came off the track and overturned, CNN+ reported.
The crash came as Valencia, Spain's third-largest city, prepared to host a visit on Saturday and Sunday by Pope Benedict XVI, for the World Meeting of the Families which will be attended by up to 1 million pilgrims.
Pallas said that the authorities had ruled out the tragedy was linked to the pope's visit.
Police sealed off streets near the station to keep crowds away as emergency team wheeled injured people into ambulances.
Recent mass transit accidents in Spain include one in Madrid in January 2005 in which about 20 people were slightly injured when a train with passengers bumped into an empty one at Madrid's Atocha station.
A more serious accident occurred in June 2003 when 19 people were killed and 48 injured in a head-on crash in central Spain. The crash, in which a passenger train collided with a freight train, occurred outside the station in the town of Chinchilla.
Bombs placed on commuter trains in Madrid by Islamic radicals killed 191 people in March 2004.