Three children required surgery for "potentially life-changing injuries" after a double-decker school bus crashed into a railway bridge near Winchester.
The top of the bus was ripped almost completely off when the vehicle hit the bridge in Wellhouse Lane in Kingsworthy on Thursday.
The bus had been taking children aged 11 to 16 to Henry Beaufort School when the accident occurred.
A Hampshire police spokesman said: "Three children received potentially life-changing injuries that required surgery."
Another 12 children were treated for minor injuries at the scene and 57 were unhurt.
Police are seeking the driver of a car that passed the bus shortly before the accident, which happened at 8.10am.
The force spokesman said: "We believe the car is a blue Ford Focus, registration ending HPX, with a roof rack and cycle carrier. The driver may have information that could help our investigation.