Western Australia faces the greatest economic losses by 2100 at $230.5 billion, while Queensland has the most properties at risk, with more than 93,000 on the line, followed by NSW with more than 71,000.
The Climate Council issued the warning on Thursday in a report estimating the financial cost of rising sea levels and storm surges, drawing on research from the University of Melbourne.
It comes one week after the United Nations warned the world would exceed 1.5 degrees of warming within years, increasing the risk of sea-level rises and more frequent extreme weather events such as heatwaves, cyclones, floods and fires.
The council's report, Rising Seas, Rising Bills, estimated the risk of sea-level rises in Australia in an intermediate scenario where global emissions peaked in 2040 and declined rapidly.
It found Australia could suffer $274.3 billion in property losses by 2100 because of inundation of low-lying areas, coastal flooding and land erosion, with effects felt in every state and the Northern Territory.
Damage to land could cost $580.7 billion, with more than 619,000 hectares of farmland at risk, along with more than 379,000 hectares of parks and recreation areas, and more than 23,000 hectares of land hosting critical infrastructure.
Scientists predicted sea levels would rise by at least another 14 centimetres by 2050, Climate Council spokesman Andrew Watkins said, but the actual figure could be higher and the risks greater.
"These are big, big numbers that we need to consider and the economic part of the study is conservative in that it doesn't account for everything that could happen but for the basic land, property and infrastructure costs," he told AAP.
"What we want is for people to realise what is at stake here."
Western Australia, with the biggest coastline, faced the biggest risk of economic loss with more than 586,000 hectares of land exposed to rising seas and storm surges.
But Queensland had the highest number of properties at risk, the report said, with the Gold Coast named the most exposed urban area in Australia, facing the loss of more than 32,000 properties and $84 billion.
Private insurance rarely covered "actions of the sea", the report noted, and could leave residents with high damage bills.
The federal government should stop approving fossil fuel projects and strengthen emission cuts to avert further risks, Mr Watkins said, but should also work with state and local governments to prevent construction in at-risk areas and preserve coastal regions.
"It is a creeping problem that's not as obvious as fire and floods and you don't want to suddenly, too late, realise what the impacts might be," he said.
"We need to plan now and the sooner we get on to it, the better."
Rising sea levels were already affecting agriculture in Australia, cane farmer Robert Quirk said.
His land in NSW's Tweed Valley sits half a metre above sea level, and rising tides mean he has to run pumps throughout the year to drain the fields.
"We have a drainage problem and for every centimetre the ocean rises, I pump another 10 Olympic swimming pools off the farm every rain event," he said.
"I've got little grandchildren who'll be alive in 2100 and what will they do?"
