Police said they were called following concerns for a woman in the sea off the coast of Brighton just before 3am.
Shoreham and Newhaven Coastguard Rescue Teams, lifeboats from Shoreham and Brighton RNLI and a search and rescue helicopter were also sent to assist.
Sussex Police have now confirmed that a Lewes woman, in her 20s, was sadly pronounced dead at hospital following the incident.
A spokesperson for the force said: “Her next of kin have been informed and our thoughts are with them at this difficult time.
“There are no suspicious circumstances and this will now be a matter for the coroner.”

1. Emergency operation on Brighton beach amid 'possible person in the water'
Photo from the scene. Photo: Sussex News and Pictures

2. Emergency operation on Brighton beach amid 'possible person in the water'
Photo from the scene. Photo: Sussex News and Pictures

3. Emergency operation on Brighton beach amid 'possible person in the water'
Photo from the scene Photo: Sussex News and Pictures

4. Emergency operation on Brighton beach amid 'possible person in the water'
Photo from the scene. Photo: Sussex News and Pictures