A paramedic and an elderly patient were killed when an ambulance crashed into a tree.
For reasons yet to be established, the ambulance left the road and hit a tree, Hampshire Police said.
The driver of the ambulance - a female paramedic - and an elderly male patient travelling in the rear of the vehicle died at the scene.
A male crew member and a male relative of the patient, who were both in the back of the ambulance, suffered serious injuries.
"Next of kin for those involved are in the process of being informed," a police spokesman said.