Three people were killed and 16 others were injured Thursday when a bus involved in a multi-vehicle crash erupted into flames in western Canada.

Oct. 16 (UPI) -- Three people were killed and more than a dozen others were injured Thursday when a bus involved in a multivehicle crash erupted into flames in western Canada, authorities said.

A total of 16 people were injured, including a police officer who responded to the scene, authorities said during a press conference.

Of those injured, 10 were transported to local hospitals, one in critical condition and nine with non-life-threatening injuries.

Five others were classified as "walking wounded," meaning they were cleared at the scene but taken to the hospital for further assessment, authorities said.

Calgary Police Service Staff Sgt. Andy Woodward told reporters that the incident occurred at about 1 p.m. MDT in northeastern Calgary.

He said a city bus collided with a white car that then crashed into other vehicles. The bus continued through an intersection and hit a city bus parked at a bus stop, causing the second bus to erupt into flames.

That second bus then crashed into additional vehicles.

At least eight vehicles were involved in the crash, according to authorities, who said the cause of the incident remains under investigation.

The second bus was powered by natural gas, which authorities said was believed to be the cause of the explosion and the subsequent fire.

"I've worked as a police officer for 36 years and I think this is probably the biggest scene that I've worked on," he said.

Calgary Fire Department Chief Steve Dongworth told reporters that the incident occurred close to a fire house and that the blaze was "a relatively quick knockdown."

Because of the threat posed by the natural gas, the hazardous materials unit was called to the scene, he added.

"It was fairly involved. It wasn't a catastrophic fire, but it was a serious fire inside, particularly the liquid natural gas bus," he said, stating there was also a small fire in the initial bus.

Canadian Prime Minister Mark Carney offered his sympathies to those affected by the crash online.

"To the families enduring this heartbreaking loss, to those recovering and to everyone grieving in the community, know that Canadians are holding you close in our hearts," he said in a statement.