A leading Kiwi climate scientist has a message for people wanting to visit Australia's Great Barrier Reef: see it now before it's too late.

Dr Jim Salinger said the "burning, drying and flooding" continent was now experiencing dramatic impacts from climate change.

"The iconic Great Barrier Reef, already badly damaged by global warming during three extreme heatwaves, in 1998, 2002 and 2016, is being yet damaged by a new bleaching event is under way now," said Salinger, currently an honorary research fellow at Otago University's Department of Geography.

"The extreme marine heatwave in 2016 killed two-thirds of the corals along a 700km stretch of the northern Great Barrier Reef, from Port Douglas to Papua New Guinea.

"It caused dramatic change for the reef and that climate change is here now.

"The message is simple - visit it now otherwise if we see more diebacks of corals in the next few years, little if any action on emissions and inadequate progress on water quality, then an 'in danger' listing in 2020 as a World Heritage area."

Salinger said the past summer had brought prolonged and at times extreme heat over New South Wales, southern Queensland, South Australia and parts of northern Victoria.

The three heatwaves across January and early February saw unusually high daily maximum and minimum temperatures for at least three consecutive days over large parts of the country.

During these heatwaves, daily maximum temperatures across southeast Australia exceeded 40C over very large areas and were typically 8C to 12C above the January and February averages.