Mayor Villaraigosa said that the number of injured remains at 135, with 81 in hospitals.
Fire official Mario Rueda says the likelihood of anyone remaining alive in the wreckage is very remote.
Emergency crews continued delicately picking apart the mangled wreckage of a commuter train that collided head-on with a freight train on the same track in Los Angeles.
The impact rammed the Metrolink engine backward into a passenger car, which rested on its side with the engine still inside it early Saturday, and accordioned the freight train cars. Two other Metrolink cars remained upright. Crews had to put out a fire under part of the train.
It was the deadliest U.S. passenger train accident in 15 years,
During the night, the teams used hydraulic jacks to keep the passenger car from falling over and other specialized rescue equipment to gently tear apart the metal.
Fire Capt. Steve Ruda said the goal was to eliminate every piece of metal and gradually work down into the passenger spaces, but by midnight crews were just getting through the top deck of the double-decker train.
"There's human beings in there and it's going to be painstaking to get them out," Ruda said. "They'll have to surgically remove them."
His firefighters had never seen such carnage, he said. The crews would have to work carefully to document the incident for investigators and so relatives could identify bodies, Ruda said.
Officials say there were 222 people on the Metrolink train and four Union Pacific employees aboard the freight train when they collided Friday afternoon in Los Angeles' San Fernando Valley.
The cause of the collision had not been determined.
"This is the worst accident I've ever seen," Los Angeles Mayor Antonio Villaraigosa said. "Clearly the injuries are going to mount and so are the fatalities."
Asked how the two trains ended up on the same track, Steven Kulm, a spokesman for the Federal Railroad Administration: "We are nowhere near having any information on that."
Kulm said the federal investigation will be headed by the National Transportation Safety Board, while his agency will conduct a review of whether any federal rail safety regulations were violated.
Union Pacific spokeswoman Zoe Richmond said it is common in California for freight and commuter trains to be on one track.
"You see it a lot in California where commuter trains share tracks with freight trains," Richmond said, adding she could not speculate about the cause of the crash.
Dr. Marc Eckstein, medical director for the city Fire Department, said 135 people were taken to hospitals - about 85 of them in serious or critical condition.
In the initial hours after the disaster, firefighters treated the injured at three triage areas near the wreck, and helicopters flew in and out of a nearby landing area on evacuation flights. Dazed and injured passengers sat on the ground and wandered about.
Leslie Burnstein saw the crash from her home and heard screams of agony as she ran through a haze of smoke toward the wreckage. She pulled victims out one by one.
"It was horrendous," said Burnstein, a psychologist. "Blood was everywhere. ... I heard people yelling, screaming in pain, begging for help."
Metrolink spokeswoman Denise Tyrrell said the Metrolink train left Union Station in downtown Los Angeles and was headed northwest to Moorpark in Ventura County. The trains collided at about 4:30 p.m. in the Chatsworth area of the San Fernando Valley, near a 500-foot(150-meter)-long tunnel underneath Stoney Point Park.
On the north side of the tunnel, there is a siding, a length of track where one train can wait for another to pass, Tyrrell said.
"I do not know what caused the wreck," said Tyrrell who broke down crying and was shaking. "Obviously two trains are not supposed to be on the same track at the same time."
Until Friday, the worst disaster in Metrolink's history occurred on Jan. 26, 2005, in suburban Glendale when a man parked a gasoline-soaked sport utility vehicle on railroad tracks. A Metrolink train struck the SUV and derailed, striking another Metrolink train traveling the other way, killing 11 people and injuring about 180 others. Juan Alvarez was convicted this year of murder for causing the crash.
That was the worst U.S. rail tragedy since March 15, 1999, when an Amtrak passenger train hit a truck and derailed near Bourbonnais, Illinois, killing 11 people and injuring more than 100.
The Sunset Limited was involved in the worst accident in Amtrak's 28-year history. On Sept. 22, 1993, 42 passengers and five crew members died when the train plunged off a trestle into a bayou near Mobile, Alabama. The trestle had been damaged minutes earlier by a towboat.