A passenger train collided head-on with a freight train on Friday near Los Angeles, killing at least two people and wounding 23, 10 of them seriously, authorities said.
The toll could rise, as six bodies under white sheets could be seen in the vicinity of the crash, according to images on local television.
The collision near the town of Chatsworth northwest of Los Angeles caused a fire and at least one car of the commuter train operated by Metrolink and seven cars from the freight train to derail, setting off a major emergency rescue effort.
The accident occured at about 2323 GMT on a curvy section of track some 31 miles (50 kilometers) northwest of Los Angeles.
The derailed passenger train car lay ripped open and on its side, with firefighters attempting to put out the flames and rescue crews working at the scene, according to live images aired on local broadcaster ABC7. At least seven cars and the locomotive of the freight train derailed.
"Clearly something went wrong," Metrolink's Denise Tyrrell told ABC7, as he confirmed the two deaths. "There was a failure somewhere along the line."
"There are many failsafes, but we're still dealing with human beings and mechanical devices, so after we have ascertained that our passengers are off that train and everyone is in good condition, then we'll start investigating the actual crash itself."
Tyrell told ABC7 that a locomotive was pulling the Metrolink train, and the force of the crash may have pushed the locomotive into the first passenger car.
It was not immediately clear how many people were aboard the Metrolink train, although typically as many as 400 people ride the line involved in the crash.
The number 111 commuter departed Los Angeles headed for Moorpark, a bedroom community 47 miles (75 kilometers) northwest of California's largest city.
Two hours after the crash, dozens of firefighters and rescue personnel were seen trying to extract people from the wreckage. Emergency helicopters airlifted the seriously wounded to hospitals.
LA Fire Department captain Armando Hogan said some 100 fire personnel responded to the accident. Many of the injuries were "mostly from people being kind of jolted around," he said.
On January 26, 2005, a Metrolink train hit a Jeep that had been parked on the train tracks in Atwater Village. The train bound for Los Angeles derailed and struck two other trains, killing 11 people.
In August the man who parked the Jeep on the tracks, Juan Manuel Alvarez, 29, was sentenced to 11 consecutive life prison terms.