Ontario Provincial Police are investigating a collision between a tractor-trailer and a school bus on Highway 12 in Severn Township, west of Orillia.
Police say the eastbound lanes are closed between Wainman Line and Prices Corner for debris cleanup.
The bus was carrying children, according to police, but no injuries have been reported at this time.
Simcoe County paramedics attended as a precaution.
Police are asking motorists to avoid the area.