A blown tire may have been the cause of a head-on crash between a semitrailer and a Greyhound passenger bus on Interstate 40 in New Mexico Thursday afternoon that left at least 8 people dead.

Authorities said many of 49 passengers board the bus were injured, although couldn’t immediately provide an exact count of how many were hurt or their conditions.

New Mexico State Police said the semi was headed east on the freeway Thursday afternoon when one of its tires blew, sending the rig carrying produce across the median and into oncoming traffic, where it slammed into the Greyhound heading to Phoenix from Albuquerque.

The National Transportation Safety Board and New Mexico state police are investigating.

Twenty patients were treated at Gallup Indian Medical Center, according to Dr. Kevin Gaines, acting chief medical officer at the hospital. Of the 20, four were children but no ages were immediately available.

At least nine patients were treated and sent to the University of New Mexico Hospital, four were transported to Banner Hospital in Phoenix and 10 were still being treated at Gallup. Conditions of those being treated at Gallup ranged from good (two patients) to serious (two) and critical (one).

At least 47 passengers were riding on the Greyhound bus that was heading from Albuquerque, with at least one scheduled stop in Phoenix, the company told the Associated Press.

The passenger bus involved in the accident experienced front-end damage, while a semi-truck was discovered lying on its side. Video also showed debris scattered about the roadway and emergency responders at the scene.

A witness described the incident as “horrible,” telling KRQE that “screams were coming from the bus.”

“It was horrible there was people trying to climb out of the windows of the bus... bystanders trying to help people getting ladders out of their truck to get to windows of Greyhound bus to assist,” the witness told the outlet. "When we went by the overturned semi, everything in the trailer was out on the road. It was a disaster...you could tell people were in distress, screams were coming from bus.”

Truck driver Santos Soto III shot video showing the front of the Greyhound sheared off and the semi split open, with its contents strewn across the highway.

He saw people sobbing on the side of the road as bystanders tried to comfort them.

"I was really traumatized myself, because I've been driving about two years and I had never seen anything like that before," Soto said.

"I'm a pretty strong person and I broke down and cried for at least 30 minutes," he added.

The crash occurred near the town of Thoreau. It forced the closure of westbound lanes of the interstate and traffic was backing up as travelers were diverted.

The Associated Press contributed to this report.