Three people have died and 19 others were injured after a chain-reaction crash involving transit buses and several vehicles in Calgary, Alberta, on Thursday, October 15, according to police.

Authorities said the collision occurred around midday on a busy city street. Investigators believe a transit bus first struck a car, triggering a series of impacts that sent the bus through an intersection and into another bus stopped at a transit stop.

The second bus, which was powered by natural gas, caught fire. The burning vehicle then crossed the road and collided with three additional vehicles, creating a major emergency response scene.

Nineteen people were injured, including 10 who were transported to hospital by ambulance. A police officer was also among those injured and taken to hospital, authorities said.

Calgary police described the crash scene as exceptionally serious. Mayor Jeromy Farkas announced that a full investigation would be conducted, while Alberta Premier Danielle Smith expressed condolences to the victims and their families.

Investigators are working to establish exactly how the collision began and what factors contributed to the chain of impacts. Further details about the victims and the cause of the crash had not been confirmed in the report available at publication time.