A spokesman for the ambulance service said it received a call at 7.05am to a stretch of beach near Marine Crescent in Goring, Worthing, and sent two ambulance cars.
They said: "Sadly, the person was beyond all help, so we confirmed the death at the scene."
Sussex Police was also called by the ambulance service.
A spokesman said the death was currently being treated as unexplained.
At 4pm, they said the woman's body 'remained unidentified'.
The death sparked an outpouring of grief on social media, with many people sharing their condolences on the Facebook page of the Worthing Herald, our sister title.
Vanessa Vermundsen said: "Unexplained and unknown circumstances aside, this is very sad and tragic for the family of this woman. Every life is precious."