Flood alerts have been issued across Queensland, with two communities urged to seek higher ground.
The state's soaking follows riverine floods in the Northern Territory where remote communities were evacuated and the town of Katherine was inundated.
The Bruce Highway in Queensland was closed on Monday in both directions north of Gin Gin, in the Wide Bay region, as a tropical low wound its way towards the southeast.
Authorities are urging motorists to postpone non-essential travel after multiple rescues of people overnight from cars driven into floodwaters.
"People should know the impact it puts on their own family and the personal strain in their community, but also think about it through the eyes of those emergency services personnel," Premier David Crisafulli said.
"They've got loved ones too and anything you can do to stay out of harm's way helps everyone."
A woman was rescued from her car after becoming trapped in fast-flowing water on Bald Knob Road in Peachester overnight.
Two other people had to be rescued in separate incidents at Goomeri, near Gympie, and Bargara, Bundaberg.
A swiftwater rescue crew was sent to save a person stranded on top of their car on the Murgon-Gayndah road.
Emergency warnings for people to seek higher ground were issued by the Central Highlands Regional Council for Sapphire at Retreat Creek and Rubyvale at Policemans Creek.
The Bureau of Meteorology has warned of significant riverine flooding across the Wide Bay, Burnett and southeast coast districts, with major warnings in place, including for the Mary River downstream of Gympie.
Rain should begin to ease overnight into Tuesday morning.
In the Northern Territory, residents in Katherine are assessing damage after their river topped major flood levels and swamped homes.
Hundreds of residents from the inundated remote communities of Daly River, Palumpa, Beswick and Jilkminggan were evacuated over the weekend, most in a major airlift by helicopters and fixed-wing aircraft.
The Daly River would continue to rise and stay at major flood level over the coming week and the river at Katherine could rise again from moderate to major flood level, the bureau's Shenagh Gamble said.
Daly River evacuees are staying at a pavilion at the Darwin Showgrounds and Palumpa evacuees are at the city's Marrara Stadium.
It is the second time Daly River residents have been evacuated to Darwin after flooding in early February.
The flooding is worse this time, with damage to homes and community services expected to be more severe.
The NT Health Department has issued a warning to Katherine residents to boil water because of the risk of contamination.
About 600 properties remained without power, incident controller Shaun Gill told reporters on Monday.
The priority was getting government buildings and shops back up and running, he said, with the closed hospital and schools being assessed for reopening.
Mayor Joanna Holden told AAP the river level was dropping and authorities were organising food drops to isolated properties.
"It's not an easy task especially if you've lost anything of great value in terms of memories, it can be quite a devastating experience for people," Ms Holden said.
"We need to look out for each other, check in on our neighbours, check in on our mates."
Lukas Fischer, manager at Katherine's Contour Hotel, told AAP the past couple of days had been stressful but hotel guests had kindly shared rooms to enable people in need to be accommodated.
"We have families who are obviously very scared of what's next ... after losing a lot of things due to the flooding," he said.
The federal and territory governments have announced disaster support payments for residents whose houses had flooded.
They range from immediate relief payments, capped at $1537 per family, to funds to replace essential household items such as white goods and furniture.
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