At least 23 people were killed, and as many as 135 people were injured when a crowded commuter train collided with a freight train outside Los Angeles Friday. Mike O'Sullivan reports that several hours after the crash, rescue workers were still pulling victims from the wreckage.

Rescue and recovery work continues as darkness begins to fall after a commuter train collided with a freight train in the Chatsworth area of Los Angeles, 12 Sept. 2008

The rush-hour train was packed with as many as 350 commuters, and was heading northwest from Los Angeles about 4:30 p.m. when it collided with a freight train in the suburb of Chatsworth.

One passenger car lay on its side with the train's engine pushed back inside it. Two other cars remained upright. The freight train's engine was also turned on its side.

Fire Chief Doug Barry said firefighters extinguished a fire in the wreckage.

"At the time that we arrived on scene, there was a fire problem, there was a hazardous materials problem with spilled fuel," he said. "We also weren't certain what was on the freight train, as well as an extrication problem, and obviously a medical problem."

He said firefighters contained the fuel spill, and were working to extricate the passengers who remained trapped in the wreckage.

Medical workers and surgeons provided treatment in triage areas set up near the site and helicopters flew the most seriously injured to hospital.

Los Angeles mayor Antonio Villaraigosa said it would take some time to assess the extent of the injuries.

"We know that dozens of people have been injured, probably over 100, but we don't have the specifics on the nature of those injuries," he explained.

Authorities say some injuries were minor, but at least 10 people were injured critically.