Startling images have emerged of devastating coral bleaching unfolding across parts of the Great Barrier Reef, as the marine park authority overseeing the environmental icon has raised its response to the highest level possible.

The severe bleaching event has again prompted concern about the damage climate change is doing to the world heritage protected reef, one of Australia's most important tourist sites, with scientists and green groups calling for Australia to lift its game in tackling global warming.

On Monday WWF-Australia released underwater images taken of bleached corals around Lizard Island in the pristine northern stretches of the barrier reef north of Cooktown.

The images were captured on Saturday, with photographs taken by members of the XL Catlin Seaview Survey and video recorded by the Queensland-based citizen science group, CoralWatch.