HM Coastguard Southend was called out at 4.10am on Sunday morning by the woman's friends.
Once at the scene the team met with Essex Police and it became clear the friends had lost sight of the female as they had run out on to the mudflats opposite Genting Casino.
A shoreline search took place with extra support being called in from the RNLI Southend Lifeboat hovercraft.
After a brief search, a police officer spotted something in the distance about 200m offshore.
A spokesman for the Southend Coastguard said: "Coastguard officers then narrowed down the search in that area and were then able to confirm the object was a possible person laying down in the mud.