About 30 people were injured — some seriously — in a rollover of a Red Arrow passenger bus in Alberta on Friday.

"There has been an incident with our coach coming in from Fort McMurray heading in to Edmonton," said Red Arrow general manager John Stepovy. "Our main concern is the well-being of passengers on the coach."

Stepovy said the vehicle was an overflow bus on the regularly scheduled Fort McMurray-Edmonton run. He said all 36 seats on the bus were full.

RCMP Sgt. Patrick Webb said some people were trapped in the bus, which rolled on Highway 28 near Redwater, about 65 kilometres northeast of Edmonton. Later reports suggested they had all been extricated.

Kerry Williamson of Alberta Health said most of the injuries were minor, but several were considered serious.

A spokesman for STARS air ambulance said two people were flown to hospitals in Edmonton. The first was a man in his 60s, said Cam Heke.

"He had sustained a very serious injury. His general condition was stable en route to the hospital.

"After transporting that patient, we then returned to the scene of the rollover and we received a second patient — an adult female, also in her 60s. She was also in stable condition; however, she had also sustained a very serious injury."

Heke didn't know if the two people were related.

Other injured passengers were taken to hospital in St. Albert, just north of Edmonton, while some were taken to the health centre in Redwater.

Williamson said a multi-casualty injury bus was sent from Edmonton to the site. The bus contains five stretchers and allows first responders to treat and triage at the scene.

"Some patients were treated on site by that bus," Williamson said.

A dozen ambulances from seven communities responded, along with police, fire and emergency rescues officials. Safety officials from Red Arrow were there as well.

Police were warning motorists that Highway 28 was closed and would remain so for several hours as the injured are treated and debris cleared. Drivers were asked to stay away.

It was sunny and dry Friday afternoon.

Highway 28 was also involved in a serious accident in May 2005 when a bus carrying oilsands workers coming home from Fort McMurray, Alta., was hit by a semi-trailer near Gibbons, just down the road from Redwater.

Six people were killed and almost two dozen were injured.