ALBUQUERQUE, N.M. (CBSNewYork/AP) – At least seven people were killed when a Greyhound bus collided head-on with a tractor-trailer in New Mexico.

Dozens more are hurt, many with serious injuries.

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“It was chaos,” New Mexico State Police Patrolman Ray Wilson said.

The front of the bus was ripped off, and wreckage from the crash was strewn across the highway.

“Just look at that bus. There’s nothing left,” said a witness. 

Investigators said it happened Thursday along Interstate 40 near the New Mexico-Arizona border. A semi-truck blew a tire, lost control and crossed the median into the path of the bus with 49 people on board.

Chris Jones was driving by moments after the crash and pulled over to help.

“There was a lot of people with injuries – from the most minor to the most severe, which you can only imagine what most severe could be,” he said. “It was a lot of screaming and yelling.”

The bus started its journey in St. Louis and its final destination was supposed to be Los Angeles. It had stopped in Albuquerque and was heading to Phoenix before the crash.

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The collision tore the tractor-trailer from the cab, turning it onto its side and spilling its contents onto the highway.

“It was as disaster. You could tell that people were distressed. Screams were coming from the bus. It was horrible,” said witness Marc Gonzales.

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Eric Huff was heading to the Grand Canyon with his girlfriend when they came across the crash. The semi’s trailer was upside down and “shredded to pieces,” and the front of the Greyhound bus was smashed, he said, with many of the seats pressed together. Part of the side of the bus was torn off, he said.

“It was an awe-inspiring, terrible scene,” 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.

Rescuers worked to free passengers trapped inside. Now, they’re working to account for all the people on board.

“It’s going to take investigators quite a while to go through and actually identify who was sitting where, who were the drivers, who were the passengers,” Wilson said.

The National Transportation Safety Board has a team headed to the site to investigate.

“We are fully cooperating with local authorities and will also complete an investigation of our own,” Greyhound spokeswoman Crystal Booker said in a statement.

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.

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(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)