Authorities are questioning a truck driver involved in a crash with a commuter train that injured 28 people north west of Los Angeles.

Scott Johnson, a spokesman for the Metrolink system whose train struck the truck at around 5.44am local time, says police in Oxnard found the driver and are questioning him.

Three cars of the five-carriage Metrolink train tumbled onto their sides in agricultural country 65 miles north west of Los Angeles.

Little was left of the truck, which stopped at a marked crossing. Some debris was in a nearby intersection and some close to the tracks.

Fire officials say four of the 28 injured are in critical condition.

Twenty-three people were unhurt.