A horrific crash between an Ottawa transit bus and a Via passenger train has left six people dead, dozens injured and many residents shaken and searching for answers as to what went wrong.

The OC Transpo Route 76 bus was heading for downtown Ottawa Wednesday morning, travelling north along the Transitway, the dedicated road for the city's buses.

Shortly before 9 a.m., the bus collided with Via Train 51, which came from Montreal and was heading west to Toronto, at a rail crossing near Woodroffe Avenue and Fallowfield Road.

​​The front end of the bus was sheared off in the collision, and five people were pronounced dead at the scene, including the driver. One bus passenger died later in hospital from injuries.

'People screamed on the bus': witness

Several witnesses said the bus failed to stop at a rail crossing moments before the collision.

Greg Mech said he was riding atop the double-decker bus when he said it crashed "dead-on" into the train. He said some people saw the train and expected the bus to stop, but it didn't.

"From what I can tell the bus driver did not notice that these train track's signal lights were on and the gates were down," said Mech.

"People screamed on the bus shortly before the crash because he was not stopping," Mech told CBC News.

Another witness, Mark Cogan, said the rail barrier was down.

"I just thought maybe there's a side way around or something but instantly he just … he smoked the train. He went through the guard rail and just hammered the train and then it was just mayhem."

Another passenger on the bus, Chad Mariage, said the bus was going the usual speed but said the driver braked just before the collision.

Mech said the aftermath was hard to witness.

"Because I was on the left side of the window, I could see that there were bodies on the train tracks. It was horrible. There's just no other way to explain it," he said.

More than 30 people were also taken to several area hospitals, including 10 in critical condition. Three people with injuries from the crash checked into hospitals themselves. Most injuries were limb or abdominal in nature.

Some of the injured have been sent home with minor scrapes and bruises, while others await surgery.

There were no serious injuries among train passengers.

'We've lost 6 of our neighbours' mayor says

Dave Woodard

Bus driver Dave Woodard, a 10-year veteran of OC Transpo, died at the scene of the crash with a Via Rail train in Ottawa on Wednesday. (Facebook)

Mayor Jim Watson called it the worst bus crash in the city's history.

"We've lost six of our neighbours," said Watson, who offered condolences to the families of the victims. "A void has been left in these lives that will be impossible to fill," he said.

Police later confirmed that the bus driver, David Woodard, 45, was among the dead. The 10-year veteran of OC Transpo was pronounced dead at the scene. 

"One of my co-workers got up today and he's not going to make it home to his family tonight and several people on his bus lost their lives as well," said OC Transpo driver Shawn Pulley.

"Every day we're out on the bus and we try to give everyone a safe ride to and from work and it didn't happen today," said Pulley.

Police said they have identified other victims but are not releasing their names until families have been properly notified.

Ottawa police and the City of Ottawa encouraged people concerned about the condition of relatives or friends they believe were on the bus to contact 311 for more information.

More than 100 people attended a vigil for the victims in Barrhaven, a community south west of Ottawa. The OC Transpo Route 76 bus makes a stop in Barrhaven, and many of those who attended the vigil told CBC News they felt it could have been them on the bus.

“It’s such a community,” one man said, adding that when photos of the victims are released, he thinks he'll recognize some of them from being out and about in the community.

Hundreds of others flocked to a vigil at the scene of the accident. Visitors lit candles, lay flowers and sang songs to remember the victims.

Canadian Blood Services said it is supplying area hospitals with additional blood to treat victims. It said it has received a number of calls from people looking to donate blood and said it is encouraging people to do so at a local blood clinic.

Investigation could take months, says TSB

Bus vs. train crash graphic

Transportation and Safety Board investigators are leading the investigation. They will look at sight lines, warning systems, gates and the locomotive event recorder as well as other recording devices that might be available in conducting its investigation, said TSB chief operating officer Jean Laporte. OC Transpo general manager John Manconi said GPS data from the bus would also be made available.

Laporte added the investigation could take several months but said the TSB would release information sooner if it could improve safety.

Ottawa police said since they began monitoring collisions in the area in 2002 there have been no crashes at the intersection of the rail crossing and the Transitway.

Craig Watson, president of the union representing Ottawa city bus drivers, said members were reeling from the driver's death.

Watson said OC Transpo drivers have not had an issue with rail crossings in the past.

"Obviously we have that concern now," he told CBC News Network anchor Carol MacNeil.

Via Rail said there were no major injuries reported on the train, but it suspended its Ottawa-Toronto service for the rest of the day. The routes would be replaced with a chartered bus service.

Woodroffe Avenue remains closed in both directions between Fallowfield and Slack roads and detours are in effect for OC Transpo buses.

With files from The Canadian Press