Police have set up safety cordons and closed several beaches around Eastbourne after explosive devices were discovered along the shore.
Beaches between Birling Gap and Cow Gap, near Beachy Head, have been closed off, police said.
The police said the explosives are thought to include a Second World War sea mine used to destroy shipping.
Police have warned the public to stay well away while the military Explosive Ordnance Disposal experts deal with the situation.
The devices were reported shortly after 4pm today (June 15) and police, coastguards and Royal National Lifeboat Institution personnel have combined to clear the immediate area.
Inspector Alex Campbell, of Sussex Police said: " Clearly there is an element of curiosity but these items are potentially very dangerous. I'd ask people to help us by staying well away from the area so that emergency services can work as quickly and efficiently as possible to neutralise any threat."
No one is reported to have been harmed, police said.