Scores of residents, some with pets, spent hours trapped on their roofs in recent days by a fast-rising river in the town of Lismore in northern New South Wales state.
The body of a woman in her 80s was found by a neighbor in her Lismore home on Tuesday, a police statement said. There were no details of how she died.
There were concerns that householders who climbed into their roof spaces through ceiling manholes could become trapped by rising waters.
A police rescue officer had saved an elderly woman from such a roof space that was almost filled with water, Lismore State Emergency Service Commander Steve Patterson said.
``He dived in through a window, noticed the manhole cover was open, when he checked, found a 93-year-old lady with about 20 centimeters (8 inches) left of space before the water hit the top,'' Patterson told Australian Broadcasting Corp.
Dozens of cars were trapped on a bridge in the nearby town of Woodburn over Monday night with both the bridge's approaches submerged.
Up to 50 people were rescued from the bridge early Tuesday, officials said.
``We had no capabilities to get them off in the dark so we just had to make sure that they bunkered down and we went in this morning and got them all out,'' Woodburn State Emergency Services Commander Ashley Slapp said.
The floodwaters are moving south into New South Wales from Queensland state in the worst disaster in the region since what was described as a once-in-a-century event in 2011.
New South Wales Premier Dominic Perrottet said there had been 1,000 rescues in his state by Tuesday and more than 6,000 calls for authorities to help.
Perrottet said 40,000 people had been ordered to evacuate, while 300,000 others had been placed under evacuation warnings.
``We'll be doing everything, we can to get everybody to safety and get these communities right across our state back on their feet as quickly as possible,'' Perrottet said.
Government meteorologist Jonathan Howe described the amount of recent rainfall in northern New South Wales and southern Queensland as ``astronomical.''
Nine of the 10 deaths reported so far were in Queensland. A 76-year-old man who disappeared with his vehicle in floodwater northwest of Brisbane on Sunday has since been confirmed dead.
Queensland Police Commissioner Katarina Carroll said emergency services held grave concerns for another man in his 70s who fell from his moored yacht in the state capital Brisbane into a swollen river on Saturday.
The cleanup was underway in Australia's third most populous city, despite more storms in the forecast for later in the week, with Brisbane Lord Mayor Adrian Schrinner urging people to register for the ``Mud Army,'' as the thousands of volunteers who mobilized to help out after the 2011 floods were dubbed.
Thousands of homes in Brisbane were inundated Sunday, many by destructive surges in swollen creeks in suburbs such as Ashgrove, where Kelvin Barfoot had to evacuate with members of his family, including his 99-year-old mother-in-law, Mina Baker, in a State Emergency Service rescue boat.
The family moved back into the top floor of their two-story home and started removing damaged furniture and electrical appliances that had been covered by almost 1.5 meters (5 feet) of floodwater.
``We thought we were pretty well prepared for it,`` said Barfoot, who leads a volunteer bush care group which has tallied more than 4,000 hours of planting and weeding along Enoggera Creek over the past six years. ``Just unbelievable. When it did start coming in, it went up very quick.''
Barfoot said his daughter and her husband swam to the house to help with the rescue after notifying emergency services that her grandmother, who moved to Australia from Christchurch, New Zealand, after earthquakes there in 2011 killed 185 people needed to get out.
``We were pretty much stuck upstairs at that point,`` Barfoot said. ``That was quite traumatic for my mother-in-law, we got her out (of New Zealand) after the earthquakes, so it was all a bit reminiscent of that for her.
``Now she's back home. She wanted to come home. She was a bit traumatized, but she's tough. She came down and asked me if there was anything to do to help!``
In a social media posted with the hashtag (hash)Rainbomb, Schrinner said the national weather agency had confirmed the six-day total rainfall for downtown Brisbane 792.8 millimeters (31.2 inches) to Monday morning was significantly higher than the previous record of 655.8 millimeters (25.8 inches) set when flooding devastated the city in 1974.
Rick Threlfall and Steve Hadley, meteorologists who moved from England to Australia and have been living in Newmarket, Brisbane, for almost a decade, were in the process of sandbagging the ground floor of their home but couldn't finish in time to beat the rapidly rising flood.
``Back in the UK, we do weather warnings for 20 millimeters (1 inch) of rain,'' Threlfall said. ``My weather gauge here has recorded 950 millimeters (37 inches) in three days. Brisbane's average is about 1,200 millimeters (47 inches) for the year, so we've pretty much had 80% of annual rainfall in three days.
``No real escaping the water, I guess.''
The extraordinary rainfall comes as the United Nation's Intergovernmental Panel on Climate Change reported this week that vast swathes of Australia have already lost 20% of its rainfall and the country's fire risk has gone beyond worst-case scenarios developed just a few years ago.
Australia's hottest and driest year on record was 2019 which ended with devastating wildfires across southeast Australia. The fires directly killed 33 people and another 400 people were killed by the smoke.
The fires also destroyed more than 3,000 homes and razed 19 million hectares (47 million acres) of farmland and forests.
But two La Nina weather patterns have since brought above-average rainfall to the same regions.
Lesley Hughes, an Australian academic and former lead author of the UN IPCC assessment reports in 2007 and 2015, said climate change was expected to overwhelm government systems such as flood responses.
``We can see that our emergency services are struggling already to cope with the floods in northern New South Wales with people stranded on roofs without food for more than 24 hours,'' Hughes said.