Four people were killed and dozens of others were injured after a bus rolled over on an “extremely icy” highway in British Columbia on Christmas Eve, authorities said.

The Royal Canadian Mounted Police said the bus crashed around 6 p.m. local time on Highway 97C east of Merritt, about 170 miles northeast of Vancouver.

The identities of the four people killed were not released and details about where the bus was traveling from, where it was headed and who owned it were not immediately available.

Emergency responders transported 52 people to hospitals. Of those, 36 chose to be treated for injuries that ranged from minor to serious, according to Michaela Swan, a spokesperson for the health care provider Interior Health.

Of those who remained hospitalized as of Sunday, two were in serious condition and two had injuries that were not life-threatening, she said.

“Although the number of patients remaining in hospital is low, this is a life-altering incident for all involved, from the initial physical injuries to the emotional and spiritual impacts of an incident such as this,” Swan said in a statement.

The RCMP said an investigation into the crash was ongoing but that “it is believed that extremely icy road conditions caused the rollover.” The temperature was about 21 degrees Fahrenheit (minus 6 Celsius) in Merritt around the time of the crash, according to weather records.

On Saturday, every province and territory in Canada had issued an emergency weather warning as a winter weather system knocked out power to thousands, slickened roads and caused the pileup of dozens of cars on a highway in Ontario.

In a statement, the premier of British Columbia, David Eby, and government ministers said they were “shocked and saddened” to hear of the crash.

“Our thoughts are with those impacted by the crash, their loved ones and the first responders and health care workers giving their all to treat people and keep them safe,” the statement said.

Adrian Dix, British Columbia’s minister of health, on Twitter thanked “everyone who answered the call of duty on Christmas Eve.”

He said that when mass-casualty protocols were activated, “health care workers from across the region rushed to assist,” including 16 ambulances and two aircraft from Kelowna, Merritt, Kamloops and surrounding areas.

This article originally appeared in The New York Times.