One person was killed and at least 265 others were injured when a Metrolink commuter train derailed south of Los Angeles this morning after a collision with a freight train, fire officials said.
The accident occurred shortly after 8 a.m. in Placentia, California, about 40 miles south of Los Angeles.
Fire officials said most of those hurt suffered minor injuries and were being treated at the scene.
Orange County Fire Authority spokesman Mr Gary Layman said at least 265 people were injured and that 25 people were taken to area hospitals with more serious injuries.
One person was confirmed dead but his identity was not immediately available, officials said.
The southbound train had left the Orange County city of Riverside and was headed for San Juan Capistrano when it was rear-ended by a freight train traveling on the same track in the same direction, Mr Layman said.
Two of the train's three passenger cars derailed but remained upright on the tracks, Mr Layman said. The track did not appear damaged but one of the cars crumpled up and came off the track.
Passengers at the scene described feeling the train stop just prior to the impact which caused one of the two derailed cars to crumple at the point of impact and jump halfway off the track.
Mr Patrick Madden, 37, an insurance broker who takes the train from Corona to Anaheim, said, "We were stopped at a light when all of a sudden I heard a big boom and then I felt a shock wave go through the train.
"People went flying out of their seats. People were moaning and groaning in pain. My friend hit a table and broke his ribs. There was blood and pillows and people and train schedules everywhere and then I just kind of stumbled off the train."
Emergency workers set up a makeshift triage area some 30 feet from the tracks where passengers could be seen lying on large tarps receiving treatment for injuries ranging from cuts and bruises to back injuries, sore necks and broken bones.
Other passengers could be seen wandering around the area looking dazed and bewildered, wearing business suits and carrying briefcases.
The cause of the crash was under investigation.