Half the Great Barrier Reef's coral has disappeared in the past 27 years and less than a quarter could be left within a decade unless action is taken, a landmark study has found.

A long-term investigation of the reef by scientists at Townsville's Australian Institute of Marine Science found coral had been wiped out by intense tropical cyclones, a native species of starfish and coral bleaching.

Australian Institute of Marine Science senior scientist Hugh Sweatman says the reef's health has decreased dramatically.

Researchers warned that while the World Heritage listed reef was a dynamic system — with coral cover rising and falling over time — if the mass die-off continued less than 25 per cent would exist in 2022.

"The big concern going forward is that if nothing else changes than within 20 years the reef could be in a perilous state," said institute senior scientist Peter Doherty .