At least two people were killed and 36 more injured after a charter bus overturned on the Bush Turnpike near Dallas on Thursday morning.

The charter bus was carrying 45 passengers, emergency crews told the NBC Dallas-Fort Worth affiliate.

The bus rolled over near Belt Line Road on Texas State Highway 161/President George Bush Turnpike after it slid onto the other side of the highway, according to the Texas Department of Public Safety. It’s unclear what caused the bus to veer.

Traffic was backed up on the highway for several miles, and early reports indicated that the passengers on the charter bus were trapped inside the vehicle as emergency crews responded to the scene.

The injured were taken to Las Colinas Medical Center, which received six patients, as well as Baylor Medical Center. Both hospitals are located in Irving.

The bus involved in the crash is owned by Cardinal Coach Line, a company based in Mansfield, Texas, according to the Associated Press. An employee of the coach bus company didn't answer questions about the accident.

The bus was on its way to the Choctaw Casino Resort in Durant, Okla., passenger Dan Risik, told NBC. He said most of the passengers were retirees and senior citizens, and that their bodies were lying on top of each other after the bus rolled over.

Robert Hare, who said he witnessed the aftermath of the crash, stopped to help the injured.

"A lot of people in shock, broken bones. A couple of people who are dead. They were crushed under the bus,” he said. “"You see this bus on the side of the road, and what can you do? You just stop, you get out and you do whatever you can to help."

Ed Cluck said he first saw a plume of white smoke, and originally thought the smoke was emanating from a street sweeper.

"Cars started slowing down and you realized it was a vehicle on its side," he said. "And obviously a big one, stopped jumped out and got to the front of the vehicle, you look into see who you could help, and it was just people stacked on top of each other.”

The highway was shut down following the incident, with the Department of Public Safety saying the closure would last several hours.

RELATED STORIES