The accident, which involved two semi-trailer trucks, a bus carrying seniors and three cars, happened at about 6:30 p.m. PT near Exit 355 about 15 kilometres south of Kamloops.
Police have only confirmed a vehicle slid on a curve, blocked the highway and caused a chain reaction.
According to one unconfirmed report, the incident began when one of the semis clipped an SUV. The semi driver was out of his truck and talking with the other driver when his rig was hit by the northbound bus.
Then a logging truck slammed into the back of the bus, carrying that vehicle and the truck driver at least 15 metres down the very slushy and icy highway. At least two cars subsequently rammed the wreckage.
The man driving one of the trucks was taken to hospital in critical condition. He was flown to hospital in Vancouver for surgery for multiple fractures to his lower body.
Police say a handful of seniors and one passenger in another car were treated for minor injuries. Other than the truck driver, everyone else had been released from hospital by Thursday afternoon.
Seniors trapped in bus wreckage
Kamloops Fire and Rescue assistant Chief Dave McMahon said the bus, carrying as many as 35 seniors, was wedged against a semi-trailer, trapping passengers in the vehicle. He said the jaws of life had to be used.
"We had to remove the front windshield of the bus to be able to get passengers out. Fortunately there were no real serious injuries," he said.
McMahon said the roads were slick at the time of the crash.
The northbound lanes of the Coquihalla Highway were closed for much of the night while crews cleared the wreckage and reopened by 8 a.m. PT Thursday.
Dangerous mountain highway
The mountain highway is one of the main transportation routes connecting the West Coast with the interior of the province and the rest of the country, but it has a reputation for treacherous winter driving conditions and avalanches.
B.C.'s Transportation Ministry issued a statement saying the contractor, Argo Road Maintenance, which is responsible for snow clearing along that section of highway, has "a great record for winter maintenance" on the Coquihalla, and they were satisfied with how the latest snowfall was handled.
"There was an exceptional dump of snow in this area early yesterday evening — reports of as much as 20 cm in a half an hour. This was an isolated and localized severe storm event that resulted in snow-covered roads and poor visibility," the statement said.
"The maintenance contractor already had equipment out in the area, and quickly mobilized additional equipment as the weather worsened. Our staff were very satisfied with their response to the snowfall event and their management of the incident site in co-operation with emergency responders."