A cyclist in her 50s is in hospital in critical condition after she was hit by a bus on Park Ave. Thursday night.

The woman appears to have swerved into the path of the bus heading north when she tried to avoid hitting a car door that suddenly opened at the corner of St-Viateur St.

Witnesses also said she wasn't wearing a helmet.

“The bus was right behind her. The bus hit her from behind. She was ejected from her bicycle and started doing somersaults,” said witness Simon Drapeau.

Police say the exact sequence of events remains unclear, and there are many witnesses reporting slightly different versions of what happened.

Collision investigators were called to the scene to reconstruct the crash.

“Did she actually hit the door, fall off the bike and then there was contact with the bus that was driving north? How did all this happen, that's what we’re still waiting to figure out,” said Montreal police spokesperson Anie Lemieux.

Witnesses said the bus driver swerved and jammed on the brakes to avoid crushing the woman underneath the wheels of the bus.

“Half the people on the bus actually fell out of their seats or if they were standing fell to the floor,” said witness Davesh Patel.

Many cyclists passing by expressed frustration about the collision – and the car door that may have caused it.

“It's probably the worst situation that can happen to a cyclist because you have no control over the situation,” said one passing cyclist.

“It doesn't take much to look over your shoulder, open your door a little bit and peek out. I'm also a driver, so you just have to look for cyclists all the time,” said another.