20/03/2016 12:34 PM AEDT | Updated 15/07/2016 12:51 PM AEST

'I'm Witnessing The Death Of A Large Section Of The Reef': Academic

James Morgan via Getty Images
An inshore reef seen from the air, Queensland, Great Barrier Reef.

Australia needs to do better.

That's the message from a leading marine expert who says the federal government must act urgently to save the Great Barrier Reef from the devastating scourge of coral bleaching.

"I'm up on Lizard Island right now and witnessing what I'm pretty sure is the worst bleach I've ever seen," University of Queensland marine researcher Justin Marshall said on Sunday.

"It's definitely to do with burning too much fossil fuel. Unfortunately this year we also have a natural El Nino event, so the two combined to give us this very severe bleach."

Queensland's world-famous reef has degraded over the past 20 years due to coral bleaching, which is caused by heat stress resulting from high sea temperatures.

Some of the blame for the unsightly blight has also been attributed to the dredging and dumping of sediment along the Queensland coast.

The reef previously suffered serious outbreaks of coral bleaching in 1998 and 2002.

Environment Minister Greg Hunt will reportedly tour the region on Sunday and is expected to upgrade the threat level from the coral bleaching to its highest level.

Marshall told ABC television he was shocked at what he was seeing at the World Heritage Area.

"I'm definitely witnessing the death of some of the Great Barrier Reef but unfortunately we have this unknown figure, how much is going to recover," said the researcher, who's been visiting the reef for 30 years.

He called on Hunt to do more to address the problem and urged Australians to visit to reef to see the impact of coral bleaching for themselves.

"Australians, I think we need to step up. I would encourage any Australian to come out and look at the reef right now," he said.

"I really hope that some of it -- much of it -- will recover but that's in the hands of people like Greg Hunt and other fellows around him and I think they need to do better."

Marshall's comments come after James Cook University researcher Terry Hughes earlier this month urged the government to divert some money allocated for the purchase of military submarines to the reef.

The defence contract is worth $50 billion for the acquisition of 12 submarines.

"The Australian government has plans to buy 12 submarines. If we only bought 10, we could have a much better management plan for the Great Barrier Reef than we currently have," Hughes told the Brisbane Times.

"The question is, 'do we have the right policy settings, the right legal frameworks, the correct institutional arrangements to secure a future for the Great Barrier Reef?'

"In my opinion, we don't."

Meanwhile, the Climate Council on Sunday released its latest report showing "exceptionally long and hot warm spells" in March broke records across the nation's southeast.

The report found that in the first four days of the month, maximum temperatures were at least four degrees Celsius above average over much of Australia, and up to 12 degrees above average over most of the country's south-east.

Climate Council chief councillor Tim Flannery described the conditions as "unprecedented".

"These warm conditions throughout the earth now are really having an impact on humanity in so many ways. Droughts, enhanced fire conditions, changed rainfall patterns, shrinking glaciers," he said.

"We are now living in a new climate and the heat marches on tries to deal that."