A bus passenger involved in a multi-vehicle crash that left more than two dozen people injured on Coquihalla Highway on Sunday said the pileup happened so fast, he's not even sure where it started.

"All of a sudden we found ourselves overturned," said Jordan Kawchuk, who was taking the Greyhound home to Vancouver after visiting his daughters in Kelowna.

The crash Sunday night left this bus on its side in a ditch off the side of the Coquihalla Highway north of Hope, B.C. (Shane MacKichan)

"I recall everybody standing up on an angle and people yelling, 'Get to the right, get to the right!' so we wouldn't tip further."

The bus was tilted to the side, balancing on two wheels, when a semi came barrelling down.

"It was our bus driver who said, over the intercom, 'Brace yourselves.' Then there was what seemed like a long silence, and then boom. Something hit us, which I now know was a semi truck," Kawchuk said.

"People went flying."

The crash involved two buses, two transport trucks and two passenger vehicles. Twenty-nine people were injured. (Shane Mackichan)

Lacey Shepherd was also on the bus and caught the moment a semi came flying into the pileup.

The video catches passengers screaming as the semi skids down the road, with a yell for everyone to brace themselves just before the truck hits.

Watch the video below:

After their own bus crashed, Greyhound passengers watched as a semi careened into the pileup on the Coquihalla Highway on Sunday. 0:18

Shepherd said she was "very sore and still shaken up" on Monday, but otherwise unhurt.

In all, two buses, two semi-trailers and two vehicles were caught up in the crash just south of the Othello Road exit just after 8 p.m. PT. RCMP said winter conditions played a major role in the chain reaction crash.

Twenty-nine people were taken to hospital. B.C. Emergency Health Services (BCEHS) said their conditions ranged from stable to critical.

Another 136 people who weren't injured — including Kawchuk — were taken to Hope Secondary School to warm up.

Responders worked for hours in the snow to free people trapped in vehicles. BCEHS said 22 ground and air ambulances were sent to the scene.

Jordan Kawchuk took this photo inside Hope Secondary School on Sunday night. The school became an impromptu warming centre for more than 130 people after the crash. (Jordan Kawchuk)

RCMP Const. Mike Halskov said that on a scale of 1 to 10, the crash is off the charts.

"I would rank this one as an 11 as far as the number of vehicles and people involved. It's a very significant crash," he said. "With the sheer number of people involved, trying to identify everybody, what vehicle they're associated to ... it's fairly complex, that's for sure."​

Three fire departments and four search and rescue teams also responded. Mario Levesque, who manages Hope Search and Rescue, said vehicles were sprawled across both lanes and into bordering ditches.

Fire crews and search and rescue teams pulled several trapped people from vehicles after the crash. In all, more than half a dozen emergency response teams from at least three jurisdictions were on scene. (Shane MacKichan)

He said rescues were delicate because of the way vehicles were propped up against each other — a bad move could've created a disastrous chain reaction collapse.

"We had one individual who was in one of the tractor-trailers and basically underneath the other tractor-trailer," Levesque said.

"We had to make sure that our personnel were safe and, at the same time, making sure that if we removed part of the vehicle or removed anything, we weren't causing further or possible further injuries to the individual trapped."

Levesque praised the morale of people who'd been involved in the crash. He said they stood freezing on the side of the road, helping direct rescuers to anyone who needed help.

"People were scared but at the same time ... it was nice to see people looking after each other," he said.

The highway was closed in both directions between Hope and Merritt for six hours after the crash. Northbound lanes reopened shortly before 2 a.m. PT Monday and southbound lanes opened just after 8:30 a.m.

B.C.'s Ministry of Transportation had warned drivers earlier in the day to be careful on the road due to poor visibility.

Halskov said the massive crash serves as a strong reminder to slow down and drive for the conditions.

"It is better to arrive at your destination late and safe than not at all," he said, adding that driver impairment isn't believed to be a factor.

Maintenance crews remove ice and compact snow and apply sand and salt on the Coquihalla at the crash scene on Monday. One semi, right, was still on its side in the ditch. (Emil Anderson Maintenance/Twitter)

Kawchuk said he remembers conditions on the road as "very white and snowy," but said it wasn't anything he hasn't taken the bus through before.

Greyhound Canada confirmed one of its buses was involved in the crash. It said 51 people, including the driver, were aboard.

The company said it would be launching its own investigation into what happened.

With files from CBC Daybreak South