At least seven people were killed and many others injured when a semitrailer crashed head-on with a commercial passenger bus along Interstate 40 in New Mexico near the Arizona border in the town of Thoreau.

Interstate 40 was shut down for nearly eight hours, according to CBS News. Traffic backed up as travelers were diverted around the accident scene. New Mexico State Police reported that the semi was traveling east on the freeway in late August when one of its tires blew. The impact sent the semi, which was reportedly carrying produce, across the median into oncoming traffic, where it slammed into the Greyhound bus, originally headed to Phoenix from Albuquerque.

At least nine passengers were treated at the University of New Mexico Hospital. Witnesses described a chaotic, horrific scene with passengers on the ground and people screaming.

Eyewitness Chris Jones was traveling west on Interstate 40 when he saw the semi turned over. He stopped to help and encountered the driver of the semi-sitting on the side of the highway. He reported that the driver told him that one of his front tires had popped, forcing the truck to veer into oncoming traffic, where it struck the bus.

When a tire blowout occurs, the instant loss of tire pressure makes it difficult or even impossible for the driver to maintain control. According to a personal injury lawyer in West Palm Beach, “Tires cause approximately 11,000 vehicle accidents every year in the United States. In 2016, malfunctioning tires caused 733 U.S. fatalities and about 19,000 injuries.”

KRQE reported witness Marc Gonzalez’s statement: “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 the Greyhound bus to assist. 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 the bus.”

Eric Huff, another witness, was heading to the Grand Canyon with his girlfriend when they encountered the accident. He said the semi’s trailer was upside down and shredded to pieces, and the front of the passenger bus was smashed, with many of the seats pushed together. Part of the side of the bus was torn off. He referred to it as, “…an awe-inspiring terrible scene.”

Another truck driver came upon the scene and said he was traumatized by what he saw. “I’m a pretty strong person and I broke down and cried for at least 30 minutes,“ he reported, adding, “I’ve been driving about two years and I had never seen anything like that before.”

The accident is still being investigated by the National Transportation Safety Board and New Mexico State Police. Greyhound spokeswoman Crystal Booker assured that they are in full cooperation with local authorities and will also complete their own separate investigation.

The truck driver is expected to recover