A passenger on a transit bus in Edmonton is in critical condition after police say she fell out the vehicle鈥檚 back door.

Police say the bus was making a left turn in the city鈥檚 west end on Friday afternoon when a 63-year-old woman stood up from her seat and moved towards the rear exit.

They say she reached for and held onto a safety bar, but as the bus turned, she lost her balance and fell backwards through the door and onto the street.

鈥淧aramedics treated and transported the woman to hospital with serious injuries. Sadly, her condition rapidly declined in hospital, where she remains in critical condition,鈥� police said in a statement Sunday.

They say they are still investigating but that no Traffic Safety Act charges are pending at this time.

The Edmonton Transit Service said in a statement that it is supporting police in their investigation, and that it has also reported the incident to the province.

City spokeswoman Jennifer Badry said the exit doors of buses lock when the vehicles are in motion, but the woman fell against the glass in the door, the glass shattered and she fell through it.

鈥淚t looks like she lost her balance and fell into the glass and that鈥檚 what gave way,鈥� Badry said in an interview.

The ETS statement said the service will conduct an engineering assessment 鈥渋ncluding a root cause analysis out of an abundance of caution as rider safety remains our utmost priority.鈥�

The statement said the nine-metre-long community bus was travelling at low speed at the time and that it stopped immediately.

It said the service 鈥渆xtends its sincerest empathetic condolences鈥� to the family and friends of the rider.