LOS ANGELES—A commuter train carrying 222 people collided head-on with a freight train during the Friday afternoon rush, killing at least 10 people, injuring dozens and trapping an unknown number of others in a passenger car crushed by its own engine.

Firefighters extinguished a blaze under part of the wreckage and were working hours after the collision to free people from the destroyed commuter car, which was left toppled on its side with the train’s engine shoved back inside it. Two other cars in the Metrolink train remained upright.

The Union Pacific freight train’s engine was also turned onto its side, with the rest of the train splayed out like an accordion behind it.

Mayor Antonio Villaraigosa told reporters at the scene that 10 people were confirmed dead and that the toll could go to 15. He said the number of injured was probably more than 100.

“This is the worst accident I’ve ever seen,” Villaraigosa said. “Clearly the injuries are going to mount and so are the fatalities.”

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

Fire Chief Dennis Barry said the Metrolink locomotive was deeply embedded into the passenger car.

“We have victims on top of victims,” Barry said.

The crash “made a terrible sound, like a bomb, a huge noise,” said Julio Pedraza, 35, who lives and works at a nearby horse boarding facility. He said he saw passengers emerging from the wreckage, and he and others helped the injured, one with skin peeling off of his forehead.

“They were yelling for help and crying,” Pedraza said in Spanish.

Firefighters treated the injured at three triage areas near the wreck, and helicopters flew in and out of a nearby landing area on medical evacuation flights.

Rescuers worked atop the wreckage and through breaches in the passenger car to reach victims. Dazed and injured passengers sat on the ground and milled about on both sides of the tracks.