Images of the crash during the afternoon rush hour showed upper deck seats hanging from a gaping hole at the front of the bus, firefighters on ladders trying to reach the injured and a lineup of 25 ambulances waiting in the biting cold to take them to hospitals.
The investigation will take a long time and likely would mean the closure of the busway and nearby roads for at least many hours, Bordeleau said.
Ottawa Mayor Jim Watson said more than 20 people had been injured in the collision, noting some of them remain in critical condition.
According to the Ottawa Citizen, the bus was travelling west on the Transitway at around 3:50 p.m. on Friday when the crash occurred.
In a press conference, Ottawa's Police Chief said the most serious injuries involved people sitting on the second-level of the bus.
Gabriel Rivett-Carnac, an eyewitness who lives across the street from the station, told CTV News' Annie Bergeron-Oliver that "an unusual number of sirens" alerted him to the incident. However, he also said the driver of the bus had been detained for questioning.
"Based on the way it looked, if there was anybody at the front of the bus at the top ..."
"Our hearts and condolences go out to all those injured, those family members who have lost loved ones and their families", Watson said.
"I saw bodies flying out and it was pretty intense at the time", Borle said.
"I haven't seen something of this magnitude before", he said. "It's not a comfortable thing to witness and I can't imagine experiencing it". "My first thoughts are with those who have been injured and their families". "Westboro station is still an active emergency site, and I would ask residents to stay out of the way in order to assist first responders with their work". A double-decker commuter bus crashed into a passenger train in September 2013, killing six people including the bus driver.