Ottawa police are responding to what they called a "serious bus collision" at Westboro Station on the Transitway late Friday afternoon, with several people critically injured.
The city's police chief Charles Bordeleau said the bus driver was arrested at the scene and taken in for questioning.
The crash took place west of downtown at 3:50 p.m., at the beginning of rush hour, just as dusk was beginning to settle on the coldest day of the winter so far in the capital.
Government officials on all levels are offering thoughts and condolences for the victims, as well as thanks to first responders after a double-decker OC Transpo bus collision, which claimed three lives at Ottawa's Westboro Station. Their names have not been released.
OC Transpo said its Saturday routes serving Westboro and Dominion stations are on detour between Lincoln Fields and Tunney's Pasture stations due to the shutdown.
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Paramedics said a total of 25 people were taken to hospital, suggesting one of the victims could not be revived at the scene and the other two died after arriving.
The Ottawa Hospital said seven of its patients are in critical condition, and nine are in stable condition, across both campuses.
"We're taking every necessary step to establish all of the facts and will co-operate fully with any investigation", said John Manconi, the general manager of Ottawa's transit service, OC Transpo. "Our investigators will be working through the night and into the morning to document the scene".
Witnesses described passengers being flung from the top of the bus out the front window. "And there was a bit of blood on the floor", Bilal Gill said. "There was definitely people pinned".
Anyone looking for information about family members can go to the Churchill Seniors Centre at 345 Richmond Rd.