RCMP in Merritt, B.C., say six people are in critical condition and 15 are in serious condition after a tour bus crashed on a mountain highway Thursday afternoon.

The crash happened around 3 p.m. on the Coquihalla Highway about 30 kilometres southwest of town.

It appears the bus, which was carrying 56 people from the Okanagan to the Lower Mainland, may have rolled over.

RCMP Sgt. Norm Flemming said the cause of the accident is under investigation and that only one vehicle was involved.

One witness, who did not see the crash, told CTV Vancouver that the bus passed them at a high speed.

The RCMP said there were both Canadian and non-Canadian passengers onboard and all suffered at least minor injuries.

Kelowna General Hospital was expecting some patients while approximately 40 were taken Royal Inland Hospital in Kamloops.

The highway was closed Thursday evening. Air ambulances were landing on the roadway.

With files from The Canadian Press