Four firefighters died in a road crash as they headed home from battling wildfires in Canada's westernmost British Columbia province, police said Wednesday.

The pickup truck they were traveling in collided head-on with a large semi-trailer truck on the Trans-Canada highway west of Kamloops in the early hours of Tuesday morning, Royal Canadian Mounted Police Corporal James Grandy told AFP.

All four, men in their 20s and 30s, were pronounced dead at the scene, while the driver of the semi-trailer managed to escape his rig, which had caught fire. He was taken to hospital for non-life-threatening injuries.

"We don't really know what the cause of the crash was, but the initial indication is that the pickup truck... failed to navigate a turn in the highway and crossed over the center line and struck the oncoming semi-trailer," he said.

The four firefighters, he added, "had finished work for the day and were heading home." 

They had been hired as subcontractors by the British Columbia Wildfire Service to help with wildfire suppression efforts in the area.

Four people have died this year fighting record wildfires in Canada, including a helicopter pilot.

The fires have scorched more than 17.6 million hectares across the country and displaced 200,000 including the entire city of Yellowknife in the far north, and suburbs of Halifax on the Atlantic coast and Kelowna in British Columbia.