Thousands of people could be isolated for days at the Queensland regional hub of Bundaberg after the Burnett River burst its banks, triggering memories of a 2010 disaster.
More than 400 homes and businesses are under threat, with the river set to peak at 7.6 metres early on Wednesday.
It is only just below the 7.92m levels of 16 years earlier when the city of more than 70,000 people was inundated and hundreds forced to evacuate.
Locals were asked to leave immediately late on Tuesday before the community's two major bridges were shut down, leaving about 10,000 people isolated - potentially for a number of days.
Bundaberg Mayor Helen Blackburn acknowledged the mental health impacts on people who had been caught up in previous floods and implored them to put their personal safety first.
"We're not new to this, we've done it before," she said.
"We can replace possessions. We can't replace people."
Water rescue crews and extra emergency services, including more than 30 police officers, have been sent to the Bundaberg region in preparation.
Almost 800 roads across Queensland have been cut by floodwaters after a tropical low left a trail of destruction, claiming about 1000 livestock.
Flooding has also affected the Northern Territory.
More rain has stalled the clean-up at Katherine, where hundreds of people remain in shelters, houses are still without power and crocodiles have been spotted in floodwaters.
Hundreds of residents from the communities of Daly River, Palumpa, Beswick and Jilkminggan were airlifted at the weekend, mostly to Darwin.
Residents in the NT capital have been asked to minimise water use after flooding shut down a Darwin River Dam pump station.
Temporary generators have been put in place, with the full water supply set to return in the coming days.
Darwin residents have been thanked for restricting use but water pressure is still set to be reduced in homes on Wednesday to cope as the pump station is fixed.
Flood watches were in place across much of the NT, particularly on the Top End's northwest coast including Darwin, the Bureau of Meteorology said.
"Within this flood watch area, any river, creek, lagoon, billabong, any waterway, is going to be very, very responsive to heavy falls that can occur," the bureau's Shenage Gamble told reporters on Tuesday.
That could readily lead to localised and flash flooding, she said.
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