The RNLI, police and the coastguard have been despatched to the scene.
The RNLI lifeboat in Shoreham was called out to the incident within the last hour.
Police officers were seen on the beach in East Preston, as well as members of the coastguard.
A spokesperson for HM Coastguard said: “HM Coastguard received a request for assistance from Sussex Police with an incident at East Preston beach just after 2.10pm today (December 22).
“A coastguard helicopter, Littlehampton Coastguard Rescue Team and Shoreham RNLI lifeboats have been sent.”
An RNLI spokesperson said that Shoreham RNLI lifeboat station launched its lifeboat at 2.35pm.
Sussex Police has been approached for a comment.

1. SEA SEARCH EAST PRESTON 13.jpg
The RNLI, police and coastguard have been called out to an incident in East Preston. Picture: Sussex News and Pictures Photo: Sussex News and Pictures

2. SEA SEARCH EAST PRESTON 5.jpg
The RNLI, police and coastguard have been called out to an incident in East Preston. Picture: Sussex News and Pictures Photo: Sussex News and Pictures

3. SEA SEARCH EAST PRESTON 10.jpg
The RNLI, police and coastguard have been called out to an incident in East Preston. Picture: Sussex News and Pictures Photo: Sussex News and Pictures

4. SEA SEARCH EAST PRESTON 18.jpg
The RNLI, police and coastguard have been called out to an incident in East Preston. Picture: Sussex News and Pictures Photo: Sussex News and Pictures