The sightseeing bus overturned en route to the glacier near the Columbia Icefield in Alberta’s Jasper National Park, according to the report.

CBC News said the incident involved one of the off-road buses that ferry visitors onto the glacier, owned by Pursuit, the company that operates tours of the ice fields, which are part of the Athabasca Glacier.

Three adults were killed out of the 27 passengers, and several emergency workers and fire departments were descending on the scene, the report said, citing The Royal Canadian Mounted Police (RCMP).

Critically injured passengers were being transported from the crash site to various Alberta hospitals on helicopter ambulances, it said.

The report said several hospitals in the province were preparing to receive patients, some in critical or serious condition, citing a spokesperson for Alberta Health Services.

RCMP are investigating the cause of the roll-over with the support of a collision analyst, according to CBC News.