TISHOMINGO, Okla. — Six teenage students killed in a collision with a semi were riding in a small car with only four seats, the Oklahoma Highway Patrol said Wednesday.

Only the 16-year-old car’s driver and front-seat passenger were wearing seat belts when the 2015 Chevrolet Spark carrying the girls collided with the rock hauler Tuesday afternoon in Tishomingo, a rural city of about 3,000 located about 100 miles (160 kilometers) southeast of Oklahoma City, the highway patrol said.

Those killed include the 16-year-old driver, three 15-year-olds, and two 17-year-old passengers, the highway patrol said. The girls’ names weren’t released because they are juveniles.

The highway patrol identified the driver of the semi as Valendon Burton, 51, of Burneyville, Oklahoma. The report said Burton was not injured in the crash.

The crash report, released Wednesday morning, said the circumstances of the wreck remained under investigation. But OHP Trooper Shelby Humphrey said Tuesday night that the girls’ car was making a right turn when it collided with the truck, KXII-TV reported.

Tishomingo Public School Superintendent Bobby Waitman said in a Facebook post that the district had “a great loss” involving students from the district’s high school.

“Our hearts are broken, and we are grieving with our students and staff,” Waitman said.

The crash happened one week after nine people were killed — including six members of a New Mexico college’s golf team and their coach — in a crash in West Texas. In that crash, the National Transportation Safety Board determined that a 13-year-old boy was behind the wheel of a truck when it crossed the centerline and collided with a van carrying students from the University of the Southwest golf team.