Police officers from across Devon are being drafted into Torbay in case up to 10,000 revellers turn up for an unofficial beach rave party.
The event planned for Friday evening was advertised on the social networking site Facebook as a "night of mayhem".
The site now says it has been cancelled but police said the area would still be patrolled in case people turned up.
Before the cancellation, more than 4,000 people had confirmed on Facebook that they would be attending.
Police had said they expected about 10,000 people would have turned up.
"We will be monitoring the situation, and if it looks as though anything is being set up which looks like a party or an illegal gathering, we will start turning people away," a spokesman said.
"Without it being planned we haven't got the infrastructure in place"
Measures could, if necessary, include road closures and stopping people getting into the area.
And if another party began elsewhere in the force area, the officers could be moved to deal with it.
Torbay councillor Chris Lewis said such an event could be a success if it was planned in advance.
"We do believe we have got the message across that Torbay is not the place for an enormous beach party of 10,000 people.
"Maybe in the future we might plan a big event on the beach, but without it being planned we haven't got the infrastructure in place."
A post on the website warned that people attending beaches in Torbay at the weekend "will be asked to leave or be arrested".
It continued: "Do not travel to Torbay. There will still be a high police presence around the coast.
"No event whatsoever will be taking place in Torbay and we urge you to inform all others you know that are planning to attend that it is no longer going ahead.
"Sorry for any inconvenience."
It added that the Facebook page would be closed "in due course".
Police said they were "delighted" the organisers had "seen common sense and taken the responsible step".
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