Actors such as Kate Winslet and Susan Sarandon are among the stars reportedly filming at West Wittering beach.
A spokesman for the National Trust's East Head, a nature reserve in West Wittering, said: "There is a private feature film being shot on East Head," but were unable to comment further.
Susan Sarandon's next film, Blackbird, is due next year.
IMDb lists other actors on the film such as Kate Winslet, Susan Sarandon, Sam Neill, Rainn Wilson, Mia Wasikowska, Bex Taylor-Klaus, Lindsay Duncan and Anson Boon.
The films story line follows a terminally ill mother who arranges to bring her family together one last time before she dies. It is a remake of the 2014 Danish film 'Silent Heart'.