Three people were killed and nearly two dozen injured when an OC Transpo double-decker bus slammed into a bus shelter at Westboro station at the start of Friday afternoon rush hour.

The single-vehicle collision involving the westbound 269 bus to Kanata happened on the Transitway around 3:50 p.m.

During a news conference Friday evening, Ottawa Mayor Jim Watson said two passengers and one person waiting on the platform died in the "horrific" crash, and 23 were injured.

The Ottawa Hospital said shortly after 8 p.m. that seven patients were in critical condition and nine in stable condition.

One person was also taken by ambulance to the Queensway Carleton Hospital, although that patient's condition has not yet been made public. There were no patients taken to the CHEO, a pediatric health and research centre in Ottawa, indicating there were likely no children among the injured.

"Our hearts and condolences go out to all those injured [and] those family members who have lost loved ones," Watson said.

"Our thoughts are also with the others on that bus, at that station — those directly involved and those who witnessed the collision."

Flags at City Hall have been lowered to half-mast, Watson said.

Police and first responders work at Westboro station where a double-decker OC Tranpo bus struck the shelter Friday Jan. 11, 2019. (Justin Tang/The Canadian Press)

'It was chaos'

Photos of the aftermath show scenes of chaos. One shows first responders aiding an injured person on the pavement in front of the double-decker bus, its front and part of its side shorn off. The front seats of the vehicle's upper deck hang precariously from the gaping hole.

Bilal Gill was at the back of the top level of the "packed" bus when it started to swerve, then struck the shelter.

"A lot of people started screaming, [including the] people at the front who got pinned under their seats," Gill said. "It was chaos at first."

Gill said police showed up quickly and began breaking windows to free trapped riders.

"There was definitely people pinned. And there was a bit of blood on the floor," Gill said.

Driver arrested

Ottawa police Chief Charles Bordeleau told Friday night's news conference that the most serious injuries occurred on the top right side of the bus, matching images from the scene.

Bordeleau said that "something" led officers to arrest the bus driver, but didn't give specifics.

She was taken to police headquarters for further questioning, he said.

Late Friday, police released the driver pending further investigation.

Bordeleau also said it was too early to speculate about the cause of the crash, but police would be poring over video and interviewing as many witnesses as possible.

"This will be a long investigation," Bordeleau said. "Our investigators will be working through the night and into the morning to document the scene."

'Gut-wrenching' scene

Ryan Baldasso, 34, travels the route by bus daily from his home in Kanata. On Friday, his bus passed by the scene shortly after the crash.

It's horrible. You never want to see anything like that. - Ryan Baldasso

"It was pretty gut-wrenching to see. It's horrible. You never want to see anything like that. Everyone just wants to get home safe to their families and never think about stuff like this happening. It's horrible to witness something like that."

Emergency crews were called to Westboro station in Ottawa following a collision involving a double-decker OC Transpo bus. (@gabesimages/Twitter)

Police say the investigation into Friday's fatal collision involving an OC Transpo bus at Westboro station will be a long one. (@SaveOurSenators/Twitter)

'Lineup of stretchers'

Emergency crews were cutting seats and windows out of the front of the bus, likely to get at passengers, said Gabe Rivett-Carnac.

"Everyone was certainly moving fairly quickly," said Rivett-Carnac, who arrived at the station about half an hour after the crash.

"Just judging by the lineup of stretchers ... I would say they were certainly acting with some urgency."

He said he saw at least 30 emergency vehicles at the station.

'Lots of people injured here'

On Broadcastify, an online service that provides access to emergency dispatch calls, a dispatcher can be heard saying: "I'm getting a double-decker that rammed into the bus terminal. There's possibly people that are trapped in the bus. Multiple injuries."

A short time later, a first responder reports from the scene: "Just on the second floor of the double-decker bus. There's lots of people injured here."

He later reports: "We're on the side of the OC Transpo bus with a ladder trying to get people off of the second floor. … I don't know how many ambulances we have on the way, but we're going to need quite a few."

As of 6 p.m., emergency responders were still on the scene, as well as the Ottawa Police Service's collision investigation unit.

Officials from Transport Canada and Ontario's Ministry of Transportation are also investigating.

Transitway closed

OC Transpo general manager John Manconi told Friday's news conference the bus could have been holding as many as 90 passengers.

He said OC Transpo's "top priority" was the safety of its passengers and that the agency would be cooperating fully with the investigation.

As of 7:20 p.m., the Transitway was still closed in both directions between Westboro station and Tunney's Pasture station, as was Scott Street near the scene of the crash.

Drivers are being urged to avoid the area, and OC Transpo buses were still being detoured.

People seeking information about family members involved in Friday's crash can go to the Churchill Seniors Centre at 345 Richmond Rd., the City of Ottawa said.

They can also call the Canadian Red Cross at 1-855-797-8875.

With files from Denise Fung, Matthew Kupfer, Christine Maki, Joanne Chianello, Tom Parry and Trevor Pritchard