NEWMARKET — Police say a school bus carrying about 20 children has rolled over on Highway 400 southbound at Highway 9.
The Ontario Provincial Police say four people, including the bus driver, have serious but non-life threatening injuries.
Many children were able to walk away from the scene of the accident, west of Newmarket.
Emergency personnel are on scene and have closed the southbound lanes of the highway at Highway 88.
The bus was exiting Highway 9 when the incident occurred.
The collision is currently under investigation.