Australia strongly opposes a Unesco plan to list the Great Barrier Reef as "in danger" over deterioration caused by climate change.
The UN cultural agency released a draft report on Monday that recommended downgrading the reef's World Heritage status because of its dramatic coral decline, after years of public threats to do so.
Environmental campaigners said the report highlighted Australia's lack of action to curb the carbon emissions that contribute to climate change.
Australian Environment Minister Sussan Ley said the country would challenge the move.
She accused UN officials of an about-face after assurances made before the World Heritage Committee's 44th session in China next month, when the recommendation will be formally considered.
"Politics have subverted a proper process and for the World Heritage Committee to not even foreshadow this listing is, I think, appalling," she said.
Unesco did not consider the billions of dollars spent on protecting the world's largest coral reef, she said.
But the committee's draft report commended Australia's efforts to improve reef quality and its financial commitment to the site.
But it said "with the utmost concern and regret … that the long-term outlook for the ecosystem of the property has further deteriorated from poor to very poor", referring to Australia's move to downgrade the reef's health status after mass bleaching events in 2016 and 2017.
Ms Ley said she had spoken to Unesco director general Audrey Azoulay on Monday night and expressed "very clearly our strong disappointment, even bewilderment".
Placing the reef on the Unesco's in-danger list is not considered a punishment. Unesco said some sites were added to the list to bring international attention to issues and help to save them.
But some countries consider it a criticism.
Australia has resisted calls to commit to a target of net-zero carbon emissions by 2050, with Prime Minister Scott Morrison saying the country hoped to reach carbon neutral "as soon as possible" without harming its commodity-dependent economy.
The recommendation for the status of the reef prompted environmental groups to criticise the Australian government's reluctance to take stronger climate action.
The Climate Council in Australia said it brought "shame on the federal government, which is standing by as the reef declines rather than fighting to protect it".
"The recommendation from Unesco is clear and unequivocal that the Australian government is not doing enough to protect our greatest natural asset, especially on climate change," said Richard Leck, head of oceans at the Worldwide Fund for Nature.
Aside from its inestimable natural, scientific and environmental value, the 2,300-kilometre-long reef was worth an estimated $4.8 billion a year in tourism revenue for the Australian economy before the Covid-19 pandemic began.
In December, the International Union for Conservation of Nature said climate change pushed the reef into critical condition.
Imogen Zethoven, an environmental consultant at the Australian Marine Conservation Society, said the Unesco report made clear that limiting global temperature rises to 1.5°C above pre-industrial levels was critical to protect the reef.
"Australia's climate record is more consistent with a 2.5-3.0°C rise in global average temperature – a level that would destroy the Great Barrier Reef and all the world's coral reefs," she said.
The reef has now suffered three mass coral bleaching events in the past five years, losing half its corals since 1995 as ocean temperatures climbed.
Bleaching occurs when changes in ocean temperatures stress healthy corals, causing them to expel algae living in their tissues. That drains the corals of their vibrant colours and can lead to their death.
The reef has also been battered by several cyclones as climate change drives more extreme weather and there have been outbreaks of crown-of-thorns starfish, which eat the coral, in recent decades.