About 50,000 residents in New South Wales, most in Sydney's western suburbs, have been told to either evacuate or warned they might receive evacuation orders, up from Monday's 30,000, authorities said.
"This event is far from over," New South Wales Premier Dominic Perrottet told reporters. "Wherever you are, please be careful when you're driving on our roads. There are still substantial risks for flash flooding."
Prime Minister Anthony Albanese, who returned to Australia today after a week-long trip to Europe, said he would tour the affected regions on Wednesday along with Perrottet.
The federal government has declared the floods a natural disaster, helping flood-hit residents receive emergency funding support.
The latest wild storm cell - which brought a year's worth of rain in three days to some areas - is likely to ease in Sydney from Tuesday as the coastal trough moves north, the Bureau of Meteorology (BoM) said.
But the risk of flooding could remain through the week with most river catchments already near capacity even before the latest deluge. Some regions have received 800mm of rain since Saturday, eclipsing Australia's annual average rainfall of around 500mm.
About 90mm of rain could fall over six hours in the state's mid-north coast from Tuesday, reaching up to 125mm in some places, BoM said.
Winds up to 90kmh are also forecast in several flood-hit places, raising the risk of falling trees and power lines.
Battling rough seas, emergency crews continued their rescue operation on Tuesday to tow a bulk carrier ship that lost power off Sydney's coast after tow lines broke in severe weather, officials said.
Major flooding is occurring at Windsor in Sydney's west, its third and most severe flood this year, according to the weather bureau.
Footage on social media showed submerged roads and bridges, while emergency crews rescued stranded people from partially submerged vehicles that became stuck in rising waters.
Nigel Myron, a Windsor resident, said he has kept an inflatable boat ready if he had to evacuate though he is looking to move back to his place once waters recede.
"At the end of the day, what can you do? It is what it is and we dust ourselves off from the ashes and rebuild after the floods have come and gone," Myron told ABC television.
'SUBSTANTIAL ECONOMIC IMPACT'
Federal Treasurer Jim Chalmers warned the economic impact from the floods "will be substantial".
Floods have likely inundated several food-producing regions and that would hit supplies and lift prices, further straining family budgets already reeling under soaring prices of vegetables and fruits, Chalmers said.
"There's no use tiptoeing around that ... that inflation problem that we have in our economy will get worse before it gets better. It's got a lot of sources, but this (flood) will be one of them," Chalmers told Sky News.
The Reserve Bank of Australia flagged the floods "are also affecting some prices" as it raised its cash rate a hefty 50 basis points on Tuesday and flagged more tightening ahead to tame surging inflation. Read full story
The Insurance Council of Australia, which declared the floods a 'significant event', urged affected people to apply for claims, even though the full extent of damage was unknown now.
What is causing the incessant rain?
Australia has been exposed to the La Nina weather phenomenon in the Pacific Ocean two years in a row, which typically brings above average rainfall on the east coast. The La Nina event ended in June, but there is a 50-50 chance it may re-form later this year, the Bureau of Meteorology said.
Warm ocean sea surface temperatures and another phenomenon, the Indian Ocean Dipole, are bringing wetter than normal weather. The Indian Ocean Dipole index turned negative in May, increasing the chances of above average winter and spring rainfall for most of Australia, the weather bureau said in June. The Australian winter runs from June through August.
"The dice is loaded towards a high probability of rain events occurring at least in the next few months because of all those conditions," said Tom Mortlock, a senior catastrophe analyst at insurer Aon.
During a negative Indian Ocean Dipole, the eastern Indian Ocean is warmer than normal and the western Indian Ocean, near Africa, is cooler, causing more moisture-filled air to flow towards Australia.
