Wedding Cake Rock made famous by social media 'likely to collapse without warning'

A popular scenic spot south of Sydney has been cordoned off to the public, with new research revealing Wedding Cake Rock is likely to collapse without warning in the next decade.

The striking elements of Bundeena's Wedding Cake Rock - its shape and fissured white surface - could also be its potential downfall, with a geotechnical assessment showing how unstable it is.

The NSW National Parks and Wildlife Service says it carried out the investigation because of the extraordinary attention Wedding Cake Rock was receiving with people posting photographs of various stunts on its edge.

"It's only when we've had that extraordinary attention ... that it's become apparent that it's an unacceptable risk to have people close to the edge," NPWS regional manager Gary Dunnett said.

There's been a recent trend of people doing handstands near the edge and posting photos on social media.

As part of the geotechnical assessment, a drone was flown over the entire structure from top to sea level. It showed how fractured the rock is below the surface.

"(It's) given us a really, really clear picture of Wedding Cake Rock, and that is that it is likely to collapse within the next 10 years," Mr Dunnett said.

"Wedding Cake Rock is and always will be one of the absolute highlights on the Royal Coast Track and we want people to continue to come along and enjoy it, particularly during the whale watching season ... but you need to stay back."

Safety fencing will remain in place until permanent viewing platforms are installed.