VENTURA COUNTY (CNN)-
A train struck a produce truck that had parked on the tracks between the Southern California cities of Oxnard and Camarillo on Tuesday morning, Oxnard police Sgt. Marc Amon said.
Emergency personnel treated people on tarps on a road adjacent to the tracks, video from CNN affiliate KABC shows.
The truck driver fled the scene, said Sergio Martinez, a battalion chief for the Oxnard Fire Department. Authorities found him unhurt, he said.
The driver isn't under arrest because the incident is still under investigation, but authorities are questioning him, according to Amon.
At least 28 people were sent to hospitals, including four with injuries serious enough to require immediate attention, Ventura County Fire Department Capt. Mike Lindbery told CNN.
At least eight patients have been taken to Ventura County Medical Center, spokeswoman Sheila Murphy said.
The train hit the truck just before 5:45 a.m., the California Highway Patrol said online. At least one vehicle was said to be "fully engulfed," the patrol said.
Five cars derailed, three of which came to rest on their sides, said Margaret Remmen, a management assistant at the Ventura County Fire Department. Officials have completed a search of the cars, she said.
About an hour after the incident, Metrolink spokesman Scott Johnson, speaking from San Bernardino County, said that Train 102 hit the truck at Rice Avenue.
The cars did not crumple because of "collision energy management technology," in which Metrolink invested after a 2008 Chatsworth, California, crash. In that incident, a freight train collided head-on with a Metrolink commuter train, killing 25 people.
The technology, which causes the crash energy to expand outward instead of inward, probably prevented a "larger scale of injuries," Johnson said.
The train cars are also equipped with windows that emergency personnel can easily remove to evacuate passengers, he said. An hour after the crash, "a vast majority, if not all" of the passengers had been evacuated, and those injured were treated on the scene or transferred to hospitals.
"How that individual came to stop on the track is yet to be determined," he said, adding that the crash "could not be avoided from a rail standpoint."
Regarding reports that the truck's driver is in custody after fleeing the scene, Johnson said he had no information.
"I do know it was at a crossing. I don't know why a truck was there," Metrolink spokesman Jeff Lustgarten told CNN earlier.
This story is still developing, for updates, head to KTLA.com