Three people are dead and 23 people are injured after a horrific bus crash at Westboro Station on Friday afternoon.

An OC Transpo double-decker bus crashed into a bus shelter at the station around 3:50 p.m.

Two of the people killed were on the bus, and one was waiting on the platform at the station, Mayor Jim Watson said Friday evening.

The bus was route number 269 westbound, which travels between MacKenzie King bridge downtown and Bridlewood in Kanata.

Police Chief Charles Bordeleau said most of the injured passengers were on the right side of the bus's upper level.

“The upper deck of the bus was compromised and several people were trapped on the upper level for a period of time," he told a news conference.

Bordeleau said Friday the driver of the bus was arrested at the scene and would be interviewed by police.

On Saturday morning, police said the driver was "released unconditionally" pending further investigation.

The Ottawa Hospital said it received 12 patients at its Civic campus over the course of the evening on Friday and an additional six patients at the General Campus.

On Saturday, the hospital said one person remained in critical condition. Six patients were listed in serious condition and four patients are in stable condition.

Mike Sharp, a passenger who was at the back of the bus on the upper level, said passengers who were rescued by emergency services used the windows to exit the bus.

“We were really trapped at the back of the bus…there didn’t seem to be any real way to get out. We couldn’t go forward; all the seats were piled up in the front, and many of those people were pinned by the seats.

“The bus was full of people. There was nowhere to go; there was no way to escape where I was.”

Sharp said he first sensed something was wrong when the bus began rocking as it approached the station.

“The bus started to rock a little bit, almost like it bumped agains tte curb possibly, or something like that,” he said. “Then all of a sudden you kind of got a sense that it was happening a bit too much, then I looked up and the roof started caving in.”

“It was all happening very quickly,” he said. “It was very surreal. It’s all happening, all of a sudden people are starting to scream."

Investigators are asking for any witnesses to come forward with information that may help determine the cause of the crash.

The city of Ottawa said the Churchill Seniors Centre at 345 Richmond Road is open for people who are looking for information about family members involved in the crash.

The Red Cross has set up a number for people to call who are concerned about loved ones. The number is 1-855-797-8875.

Transit services general manager John Manconi said the bus could have held up to 90 passengers standing and sitting.

A witness told CTV News that he saw some passengers flung from the top level of the bus to the ground below.

Another eyewitness, Andrew Borlé was travelling downtown from Westboro this afternoon by bus, when he saw the bus going in the opposite direction crash into the station.

"I heard a bump as if the bus was going through a speed bump ... a few bodies went flying through the windshiled of the bus," he told Newstalk 580 CFRA. "There was a military man, he was just lying there."

"It was very shocking, people were screaming. I was frightened."

Political leaders from across Canada tweeted their condolences on Friday, including Prime Minister Justin Trudeau.

"I want to send my deepest condolences to the families of victims and everyone affected by today’s tragic bus crash in Ottawa," he said. "Thank you to the first responders who rushed to help - we’re monitoring the situation closely."

Ontario Premier Doug Ford tweeted: "Devastated to hear about those who lost their lives and were injured following the horrific bus collision at Westboro Station in Ottawa. My thoughts are with the victims and their families this evening. Thank you to the first responders who are working to help all those affected."Mayor Watson said city flags will be lowered to half staff.

The Transitway is closed in both directions on either side of Westboro station. Buses are being detoured to Scott Street. Scott Street is closed to cars.