Police are seeking the driver of a blue Ford Focus after a bus crashed into a bridge - leaving three children with "potentially life-changing injuries".
Hampshire Constabulary said they want to speak to whoever was in control of the car, which they say passed the coach shortly before it struck the overhead rail crossing.
The incident happened in Winchester at 8.10am on Thursday on Wellhouse Lane and the entire roof of the double decker was shorn from the frame - leaving glass and metal strewn across the road.
A statement from Hampshire Constabulary said: “Officers investigating yesterday’s serious collision in Winchester would like to speak to the driver of a car that passed the school bus shortly beforehand.”
It added: "We believe the car is a blue Ford Focus, registration ending HPX, with a roof rack and cycle carrier.
"The Serious Collision Investigation Unit is also seeking information from anyone who saw the bus on its journey from Itchen Abbas through Easton and Kingsworthy.
"Three children received potentially life-changing injuries that required surgery."
The children on board were aged 11 to 16 and all were pupils at Henry Beaufort School in Winchester.
As well as the three taken to hospital, 12 more passengers suffered minor injuries while the other 57 were unhurt.