A Metrolink train derailed in Oxnard early today after colliding with a tractor trailer on the tracks. It was a "multi-casualty" crash, officials said. Four cars derailed and at least 30 people were injured. Train cars were lying on their side at the scene, where tarps were laid out to treat the injured. The collision occurred about 5:40 a.m. at the Rice Road crossing, Metrolink spokesman Scott Johnson told the Los Angeles Times.He could not confirm initial reports of casualties. According to the CHP, at least two people were being treated for head injuries.