The coastguard helicopter and several lifeboats have been called after a man was spotted in the water off the Sussex coast.
RNLI Shoreham Lifeboat Station said a fishing boat saw a man in water between Brighton and Shoreham at about 5.50am.
A spokesman for the organisation said it is believed others may be stranded in the water.
Lifeboats from Shoreham and Brighton are currently searching the area along with the coastguard helicopters.
More to follow.