ALBUQUERQUE, N.M. (AP) — At least four people were killed and others were seriously injured Thursday in a head-on crash involving a commercial passenger bus and a semi-truck along Interstate 40 in New Mexico, near the Arizona border, authorities said.

Preliminary information indicated the semi was headed east when it blew a tire, sending the rig across the median and into oncoming traffic where it smashed into the bus, New Mexico State Police said.

There were 49 people aboard the Greyhound bus. Authorities said many were transported to hospitals, but they could not immediately provide an exact count of how many were hurt or their conditions.

Nine bus passengers were being treated at University of New Mexico Hospital with three more patients expected to be transported there later Thursday. UNM officials didn’t release any details about the patients’ conditions.

Passing motorists described a chaotic scene with passengers on the ground and people screaming.

Eric Huff was heading to the Grand Canyon with his girlfriend when they came across the crash.

Huff said the semi’s trailer was upside down and “shredded to pieces,” and the front of the Greyhound bus was smashed, with many of the seats pressed together. Part of the side of the bus was torn off, he said.

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.