Officers were called to Firestone Copse Road, Wootton, at 5pm today (January 9) following a single vehicle collision involving a motorbike.
The motorcyclist, a 43-year-old man, suffered life-threatening injuries and is currently being treated at Southampton General Hospital.
His next of kin have been informed.
Investigations into the exact circumstance of the incident are ongoing and officers are keen to speak to anyone who saw the blue motorbike travelling in the area earlier today or anyone who might have dash cam footage that could help.
The road has since been reopened.
Anyone with information can call us on 101, quoting 44200010768, or Crimestoppers anonymously on 0800 555 111.