One person was killed and another injured after they were run over by a tour bus at Castle Mountain Lookout, west of Banff, on Wednesday morning.

Police say a tour bus pulled into the view point, just before Castle Junction, at about 10:00 a.m. and the passengers got off the bus.

Two people, from Ontario, were in standing in front of the bus when it rolled towards an embankment and that’s when they were hit.

The bus rolled about 20 metres down the embankment and into the river below.

“When police and EMS arrived on the scene they located two victims of this incident. Both were found on the shore next to the bus which was completely within the Bow River,” said Cpl. Chris Blandford, Bow Valley RCMP Integrated Traffic Unit. “The preliminary investigation has determined that the bus, which was parked facing the river, had moved on its own, there was nobody on the bus, including the operator of the bus. The two victims were standing in front of the bus when they were struck.”

A 53-year-old woman died at the scene and a 55-year-old man was airlifted by STARS to Foothills Hospital in Calgary in critical condition.

Officials are looking into whether the brake on the bus was engaged at the time.

“That is part of our investigation to determine how this vehicle moved from a parked position on its own and we'll be speaking to the driver, we’ll be looking at the vehicle once it's recovered from the river to determine the settings of brakes and gearshift levers and the ignition,” said Blandford.

Police say the victims were part of a tour and there were about 20 to 25 people in the group.

“They were quite distraught,” said Blandford. “Very dramatic thing that they had just witnessed so when we arrived on the scene they were quickly pointing out where the victims were and where the bus was.”

No other injuries were reported and the remainder of the group is being looked after by victim services.