At least 15 people have died after a "very serious" road crash in the Canadian province of Manitoba, the Royal Canadian Mounted Police (RCMP) said.

The crash was between a semi-trailer truck and a bus carrying mostly elderly people.

Police said the collision happened on the Trans-Canada Highway near Carberry, two hours west of Winnipeg.

Emergency crews and air ambulances have responded to the crash.

In several tweets, the RCMP in Manitoba said it was responding to a "very serious... mass casualty" collision, and that all of its resources, including its major crime unit, had been deployed to the scene.

Emergency vehicles, including an air ambulance and 12 ambulances, were dispatched to the scene at 11:43 local time on Thursday (17:35 BST), the RCMP said at a press conference.

Most of the seniors aboard the handi-transit vehicle were from Dauphin, Manitoba and the surrounding areas.

At least 10 people, including the two drivers, are at hospital with likely "significant" injuries considering the "magnitude and force applied" from the crash, officials said.

The RCMP had asked motorists to avoid the area as several kilometres of the highway were closed near the crash site.

A witness told CBC News that he saw a burning vehicle in a ditch just after noon local time.

John Proven described the scene as "shocking". "I have never seen an accident that big," he said.

He said he also saw a semi-trailer truck nearby with a burned front end, and that about 20 police vehicles and eight ambulances were at the scene.

A spokesperson with the local air ambulance service told the news outlet that the agency had deployed one of its largest responses ever to the crash.

"This is sort of in line with the similar large incidents that we responded to in the past, such as the tragedy with Humboldt Broncos," Blake Robert said, referring to a 2018 crash between a bus carrying a youth hockey team and a semi-trailer truck that led to the death of 16 people.