Sidmouth Lifeboat is pleading with people not to venture on to East Beach, where rock falls from the crumbling cliffs are commonplace.
A similar warning has been issued by Jurassic Paddle Sports, whose staff have often witnessed cliff collapses from their position on the nearby main beach.
In a post on Facebook, Sidmouth Independent Lifeboat said: "Our Beach Lifeguards have reported numerous people walking on East Beach over the last few days.
"We cannot stress enough how dangerous it is to walk, sit or be anywhere near these cliffs. They are unstable and can collapse any time, without any warning.
"The best way to keep yourself and others out of danger is to stay off East Beach.
"For those who don’t know the area: East Beach is the beach beyond the lifeboat station and Port Royal. You have to cross the river mouth to get to it, and there are signs warning of unstable cliffs.
"Please share this post for awareness."
In Jurassic Paddle Sports' Facebook post they said: "Please follow advice from lifeguards and the warning signs and do NOT go on EAST BEACH at Sidmouth.
"The beach to the east of the river is not safe.
"The cliffs are falling down constantly and it's VERY dangerous."
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