SALT LAKE CITY (AP) — A Greyhound bus careened from a highway and plunged into a deep wash, killing a 13-year-old girl and injuring 11 other people on New Year's Eve in rural Utah, state troopers said Monday.

Investigators were still trying to determine what caused the crash along Interstate 70 west of the city of Green River.

However, a passenger reported a possible medical issue with the driver, the Utah Highway Patrol said in a news release.

The bus was heading west across the desert from Green River to Las Vegas, Trooper Jared Cornia said.

It went off the shoulder of the highway around 11 p.m. and plunged into the wash, crashing about 200 feet from the highway.

The unidentified girl was killed and the bus driver and two passengers were taken by helicopters in serious condition to hospitals in Grand Junction, Colorado, and Provo, Utah.

Cornia did not have updates on their conditions.

Eight other injured passengers were taken by ambulances to hospitals, he said.

Cornia said roads were clear and conditions were good and were not believed to have been a factor in the crash.

He said investigators were trying to obtain video from a camera aboard the bus to help determine what happened.

Lanesha Gipson, a spokeswoman for Greyhound, said the company is cooperating with authorities and conducting its own investigation.

Gipson did not have information about the driver.