At least six people died on Thursday morning in a huge car crash on an icy interstate in Fort Worth. Dozens of vehicles collided on the freeway in what firefighters called a “mass-casualty incident.” A tweet from the Forth Worth Fire Department read: “MCI alert. 1601 N Freeway. Multiple vehicles involved. Multiple people trapped.” The department followed that up with a photo of several 18-wheelers twisted in the wreckage. Authorities said at least 65 people sought treatment for injuries they’d sustained in the accident.

Department spokesperson Mike Drivdahl told NBC 5 that firefighters went car-to-car to see if anyone needed medical help. WFFA reported that crash victims were trapped on the scene because one 18-wheeler had blocked the road. Overnight sleet is reported to have turned into ice sheets on the roads. At least three more people died in overnight crashes on another nearby interstate, police said.