MONTPELIER, Ind. (AP): Two young siblings were killed when their father’s pickup truck collided head-on with a semi-tractor trailer in eastern Indiana, authorities said.

Justin Cook, 6, and Raelynn Cook, 5, were pronounced dead at the scene of Friday night’s crash in Blackford County, a few miles west of Montpelier.

Autopsies conducted Saturday found that they died from blunt force trauma, said county coroner Zach Crouch.

Their father, Robert A. Cook, 37, was seriously injured in the crash. The Montpelier man was flown by medical helicopter to a Fort Wayne hospital.

His pickup truck reportedly crossed the centerline of Indiana 18 and caught fire after it collided with the tractor-tractor. Neighbors extinguished the flames with fire extinguishers, the Star Press reported.

Authorities said Robert Cook’s pickup truck had earlier crossed the center line and nearly collided with a passenger car before it traveled into the path of the semi.

The driver of the semi tractor-trailer was not injured.

The crash remains under investigation.