OTTAWA, ONTARIO (NYTIMES) - A popular tourist outing in the Rocky Mountains in Alberta turned into a scene of chaos after a glacier tour bus rolled on Saturday afternoon (July 19), killing three passengers and injuring several of the 24 others on board, according to the Royal Canadian Mounted Police.

Corporal Leigh Drinkwater of the mounted police said that the driver of the specially designed ice bus was among the survivors although he had no knowledge of that person's condition nor that of the other injured passengers.

The bus, which has oversize tires for driving on ice and similarly oversize sightseeing windows, was climbing a rocky, steep road to the Columbia Icefields in Jasper National Park when it plunged down an embankment, Drinkwater said.

A photograph from a bystander posted by the Canadian Broadcasting Corp showed the red and white bus badly damaged and resting on its roof on rocky moraine.

It was not immediately known why the bus toppled over.

Emergency workers from a variety of agencies descended on the ice field shortly after the accident.

Helicopters contracted out by Parks Canada, the federal parks agency, were used to lift the dead and injured from the crash site to air ambulances up on the ice field or road ambulances down below on a nearby parkway.

Tanya Otis, a spokeswoman for Pursuit, the company that operates tours of the ice fields, said the incident involved one of its special, all-terrain buses that allow visitors to walk on the glacier.

Sabrina Atwal, a spokeswoman for Alberta Health Services, said that several hospitals in the province received injured passengers, including some in "critical and serious condition."

At least three helicopter ambulances were sent to the park.

The ice fields are a major international tourist attraction and are part of the Athabasca Glacier, one of the largest in the Rockies, and it feeds three major water systems in Western Canada.

While Parks Canada has said that the ice field has been melting for about 125 years, climate change has accelerated that process.

One witness said on Twitter that he was stuck with several other passenger on another "ice explorer" bus that was forced to stop after the incident.

The man wrote that he saw the other bus lose "control and roll over."

Rob Kanty, who witnessed the rollover after finishing an earlier bus tour, said in an email that it appeared the bus encountered a rock slide.

He added that the buses did not have seat belts.

Drinkwater said that investigators have ruled out any criminal intent in the crash.