RCMP in Okotoks have opened the northbound lanes of Highway 2 that were closed due to an overnight collision involving a rolled semi-trailer.

The Alberta highway was closed early Thursday morning from 338 Avenue to Highway 552. Traffic was being rerouted onto Highway 2A. The lanes were re-opened by 9 a.m.

"A northbound semi rolled blocking the north bound lanes. Northbound vehicles unaware of the rollover approached the scene and attempted to avoid the rolled vehicle and collided going into the ditch," RCMP said in a release.

"Expect delays during the morning commute while the investigation and clean up continue."

Three vehicles were involved with seven occupants. Paramedics said three people were sent to hospital with non life-threatening injuries, including a man flown by air ambulance to Calgary. A woman in her early 60s is also in Calgary's Foothills Hospital.

The driver of the semi-truck, a man in his 30s, is in hospital in High River with non life-threatening injuries.