Authorities responded to the scene and discovered the vehicle "had run into the bus platform at Westboro station", which resulted in numerous injuries on the bus and platform, according to police.
Ottawa police say they released the driver of the OC Transpo bus unconditionally pending further investigation after arresting her and bringing her in for questioning after the crash.
Witnesses told local media the OC Transpo Route 269 bus swerved moments before slamming into the bus shelter overhang at the Westboro station west of downtown.
Investigators worked through the night and identified the three victims and contacted their families, said Const. Amy Gagnon.
"That work continues this morning and no information on the identity of the three will be released at this time", a news release stated.
An investigation was opened to determine the cause of the crash, police said, adding that the bus driver was detained "and will be interviewed".
The vehicle apparently jumped the curb as it approached the station and plowed along the platform, where the roof of a shelter carved deep into the vehicle's second deck.
Ottawa Police said in a statement its collision investigation unit was on scene and is investigating. Emergency workers immediately rushed to the scene to rescue passengers who were trapped on the upper level.
Part of the Transitway, a main artery for commuters, was closed in the aftermath of the accident, and police warned people to stay away from the area.
He went outside and came across a "chaotic" scene, with at least 30 emergency vehicles, including seven or eight fire trucks, and lots of police and bystanders, he said. "I know all those impacted by this tragedy will be surrounded and supported by many", Bordeleau wrote in a tweet published late Friday evening.
The bus has a capacity of 90 people, both sitting and standing. Of those transported, 14 were in critical condition and 11 were in serious condition, paramedic chief Myles Cassidy said at a news conference.