The Prime Minister says the government will offer "enormous support" to flood-affected communities ravaged by Cyclone Debbie.
Malcolm Turnbull says Australia needs to prepare for extreme weather events like Cyclone Debbie by investing in improved infrastructure.
Mr Turnbull visited residents in the flood-ravaged Logan suburb of Eagleby, south of Brisbane, on Monday as emergency services continued cleaning up after last week's torrential rain.
Mr Turnbull said he was committed to replacing damaged infrastructure with more flood-proof buildings.
"These are record flood events so we're going to have to be better prepared for the next one because clearly this will be repeated," he said.
"We've got to make sure we are more flood-proof in the future."
Mr Turnbull said during his visit of cyclone-affected areas in north Queensland last week, it was easy to tell which buildings had been built to existing standards.
"We really now have the challenge of making sure our building standards, our planning standards, take into account that we are the land of droughts and flooding rains and fires as well," he said.
The prime minister's visit comes as police work to recover a car that was swept into the flooded Tweed River in northern NSW.
An operation is under way to retrieve the vehicle, which entered the Tweed off Dulguigan Road in Tumbulgum at 1.40pm on Monday.
It is not known if the occupants - believed to be a female driver and her two children - are alive but the car is understood to be fully submerged, a NSW Police spokeswoman told AAP.
Earlier Mr Turnbull visited the northern NSW town of Lismore, saying he was impressed by the community spirit shown in the wake of the floods.
"We have seen nature flinging her worst at Australians, but it always brings out the best in Australians," he told reporters.
"You see the resilience of the business people, the families here, cleaning up, getting on with life, getting recovery."
As many as 20,000 residents across northern NSW have been evacuated and up to 10,000 residents were without power, NSW Premier Gladys Berejiklian said.
The small indigenous community of Cabbage Tree Island was evacuated as the water rushed downstream on Saturday.
"Every effort is being made through other means of communication to advise people what's going on, and also to provide them with the best and most recent safety advice," Ms Berejiklian said.
Queensland Premier Annastacia Palaszczuk on Monday said it was still too early to know the total cost of Cyclone Debbie but that it would be "in the billions".
Queensland is expected to be hit with a total damage bill in the billions after Cyclone Debbie and ensuing floods ravaged various parts of the state.
Ms Palaszczuk said while it was still too early to pinpoint a specific figure, the destruction wrought on roads, bridges, crops and homes was huge.
Some 300 schools also need repairs after being battered by the severe weather, she said.
"In relation to the total cost ... we do expect it to be in the billions," Ms Palaszczuk said in Brisbane.
But in some good news, the flooding forecast for Rockhampton may not be as bad as previously thought.
The Bureau of Meteorology said on Monday morning the latest forecast was for a flood peak of nine metres on Wednesday, just under the 2011 flood level.
Authorities had warned over the weekend that the Fitzroy River could peak at 9.4m on Wednesday or Thursday, making it the worst flood in more than 60 years.
At that level, Rockhampton Regional Council warned 5400 properties would be under threat, including 3000 homes.
But despite the downgrade, a major flood warning still exists for the Fitzroy, with extra emergency crews sent to the town for flood preparations.
"Nine metres is still a significant event," the premier warned on Monday, telling locals they weren't out of the woods yet.
"We do want to stress to the people of Rockhampton that you still do need to make your flood preparations," she said.
But the lower peak did mean locals could breathe a sigh of relief that the Bruce Highway would not be cut, she added.
The extra SES crews will also be on hand to deal with swift-water rescues, and then rapid damage assessments after the flood has hit.
One of Rockhampton's biggest employers, Teys Australia, which operates the city's meatworks, has closed its plant in the face of the flood threat.
Teys hopes to resume processing at the plant on Friday, but warned the closure may go beyond then, depending on water levels.
"While cattle have been purchased to supply the plant for the week, the safety and wellbeing of staff is our priority. On that note we urge employees to follow the instructions of local authorities and do what is necessary to stay out of danger," the company said in a statement on Monday.
Meanwhile, Queensland State Disaster Coordinator Steve Gollschewski said authorities were conducting "exhaustive" searches for three men still missing across the state.
It comes after the body of 77-year-old Nelson Raebel was found in floodwaters in Logan on Saturday.
Queensland recovery in numbers
- About 1600 without power in southeast
- About 21,000 without power in north
- 300 schools need repairs
- 588 residences deemed uninhabitable in central and north
- 76 residences deemed uninhabitable in the southeast, likely to go up by 250-300 in coming days