Emergency responders remove a body Saturday from the Metrolink commuter train that collided with a Union Pacific freight train Friday in Chatsworth, Calif. (Rene Macura/Associated Press)

As many as 20 people are feared dead and dozens of others injured after a Los Angeles commuter train collided head-on with a freight train Friday afternoon, according to officials.

More than 220 people were aboard the Metrolink commuter train when it collided with a Union Pacific freight train around 4:30 p.m. local time.

"This is the worst accident I've ever seen," said Los Angeles Mayor Antonio Villaraigosa, saying there were 10 people confirmed dead at the scene but that the number could climb to 15. He estimated at least 100 others were injured.

"Clearly the injuries are going to mount and so are the fatalities."

Police Lt. John Romero said the death toll was between 10 and 20.

Firefighters rescue a victim from the wreckage of a Metrolink commuter train after a train crash in the Chatsworth area of Los Angeles on Friday. (Ryan Ling/Associated Press)

Firefighters worked for several hours to rescue passengers from the mangled commuter train car, which was ripped open in the accident and disengaged from the rest of the vehicle.

They also put out a fire under part of the wreckage after the engine of the Metrolink train was shoved back into the passenger car by the force of the crash.

Injured passengers were treated by firefighters at three separate triage areas around the wreckage while others were evacuated by helicopters to nearby hospitals.

"We have victims on top of victims," said fire Chief Dennis Barry.

Three people in critical condition were being treated at Los Angeles County-USC Medical Center for "massive injuries," according to chief medical officer Dr. Stephanie Hall.

Surgeons were also sent to the scene of the crash.

The freight train's engine was toppled in the accident; the remaining two commuter train cars stayed upright.

The two trains reportedly collided just after 4:30 p.m. in the Chatsworth area of the San Fernando Valley. The cause of the collision was not immediately clear, nor was it clear how the two trains ended up on the same track.

"We are nowhere near having any information on that," said Steven Kulm, a spokesman for the U.S. Federal Railroad Administration.

Metrolink spokeswoman Denise Tyrrell said the commuter train originated at Union Station in downtown Los Angeles and was headed northwest to Moorpark in Ventura County.

"I do not know what caused the wreck. Obviously two trains are not supposed to be on the same track at the same time," said Tyrrell, who broke down crying.

The toppled passenger car was part of a Bombardier BiLevel coach, a double-decker car that can seat up to 160 people.

A spokeswoman for Union Pacific said a freight train usually has a two-person crew. Their condition was unknown Friday evening.

Eleven people were killed in January 2005 when a Metrolink train struck a gas-drenched SUV that had been parked on the tracks and derailed, causing a collision with an oncoming train.

That accident, which occurred in the suburban area of Glendale, injured 180 people and led to a murder conviction this year.

One passenger from Friday's crash told a local television station that he had also been a passenger during the 2005 collision and that he was discussing it with a friend who was also riding the train when the accident occurred.

"Within an instant, I was in my friend's lap," he said of Friday's accident in an interview with KNBC-TV.

"It was so quick. It was devastating."

With files from the Associated Press