The crash at 8am on Monday involved a grey and turquoise Yamaha motorbike and a silver Ford Fiesta on Portsdown Hill Road.
The crash, which happened near the access road to Farlington Redoubt, was reported to police at 8.04am.
The motorcyclist, from Havant, sustained serious injuries that are potentially life-changing.
READ MORE: Fire service announces appointment of first female chief fire officer
Hampshire and Isle of Wight Constabulary have launched an appeal for witnesses.
A spokesperson said: “We would like to hear from anyone who witnessed the incident or perhaps saw either vehicle in the moments leading up to the collision.
“Did you see these two vehicles, or capture them on dash cam?”
Anyone with information is asked to contact police on 101, quoting 44250183211.
You can also submit information police online via the Hampshire Constabulary website.
