An "unprecedented" mass bleaching event has been recorded off Australia's western coast, scientists said Wednesday, turning huge chunks of a celebrated reef system a sickly dull white.

A months-long marine heatwave had "cooked" the sprawling Ningaloo Reef, ocean scientist Kate Quigley said, part of a world heritage-listed marine park renowned for vibrant corals and migrating whale sharks.

Although environment officials were still verifying the scale of damage, data collected by Quigley and a team of scientists found it was on track to be the reef's worst mass-bleaching event in years.

"Warm oceans have just cooked the corals this year," Quigley told AFP.

"It wouldn't be amiss to throw in the word 'unprecedented'.

"It has gone deep, it's not just the top of the reef that is bleaching. Many different species of coral are........

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