Investigators have ruled out road conditions as a factor in a bus rollover that injured dozens of people Friday in northern Alberta.

The bus was en route to Edmonton from Fort McMurray with 36 passengers when it rolled over on Highway 28 near Redwater, Alta. at about 2:15 p.m. local time.

Drugs and alcohol were not factors in the crash either, police told The Canadian Press, adding the investigation will continue.

Passengers on the Red Arrow charter bus described emerging from the wreckage to a gruesome scene. One man saw a severed hand on the pavement. Another spotted blood and clumps of hair on the road.

Twenty-eight people were transported to hospital, three remain in critical condition. Nine others were treated for their injuries on scene.

Emergency crews spent about 30 minutes trying to free five victims from the wreckage. Other passengers reportedly wiggled through the bus' emergency hatch or smashed windows to free themselves.

Most people were able to escape with minor injuries, RCMP Sgt. Patrick Webb told CTV News Channel on Saturday.

For his part, Red Arrow general manager John Stepovy said that the cause of the rollover is still unknown. The agency says it is continuing to monitor the situation.

Lalo Ramkissoon told The Canadian Press that the bus felt like it was speeding and wobbling as it rounded a curve near Redwater.

Ramkissoon said windows shattered as the bus skidded along the pavement. He said he saw some people's faces scrape along the road.

He said he and his wife consider themselves lucky. The two were treated for cuts to their hands at Fort Saskatchewan hospital and released after a few hours.

RCMP in Alberta continued their investigation into the incident on Saturday.