The man was part of a small group of six sitting on Bells Beach in Victoria when a 30-metre cliff face gave way without warning at about 2.15pm on Friday, police said.
He was one of three beachgoers struck by falling debris.
The 28-year-old man, whose name has not been released, was winched out by air ambulance and flown to Melbourne with serious upper body injuries but died before reaching hospital.
A man and a woman sustained non-life threatening arm injuries and were taken to hospital in Geelong by road.
The beach is an internationally renowned surf spot, which up until the COVID-19 pandemic, held the annual Rip Curl Pro competition.