Four bodies have been pulled from floodwater in northern New South Wales, a fertile region of rivers and valleys about 400 kilometres (250 miles) from Sydney.

The storms dumped more than six months' worth of rain over three days, according to the government weather bureau, smashing records in some areas.

In Taree, one of the worst-hit towns, the swollen Manning River broke a 96-year record.

People picked through piles of sodden trash dumped in the town centre, searching for anything salvageable.

Rescue worker Jason Harvey said the immediate flood emergency was over but the clean up had just begun.

"Emotions were high as we were rescuing a lot of people who are distraught when we get to them," he told AFP.

"We are now at that clean up stage. I am glad it is over," he said.

The rising tides cut off tens of thousands of people, forcing some to clamber atop cars, houses and highway bridges before helicopters winched them away.

Rescue crews have plucked more than 600 people to safety since the waters started rising earlier this week.

State Emergency Service head Dallas Burnes warned that even as the floods recede, the stagnant, muddy lakes still poses a threat, including from snakes that may have slithered into homes.

"Floodwaters have contaminants. There can be vermin, snakes. You need to assess those risks.

"Electricity can also pose a danger as well."

He said recovery efforts were focused on "resupplying the isolated communities".

-'Horrific' circumstances -

As he travelled into the disaster zone on Friday, Prime Minister Anthony Albanese described the situation as "horrific".

"The Australian Defence Force will be made available. There's going to be a big recovery effort required," he told local radio.

"There's been massive damage to infrastructure and we're going to have to all really pitch in."

The government has declared the floods a natural disaster, unlocking greater resources for affected areas.

About 50,000 people had been cut off from help at the height of the disaster, authorities said.

Business owner Jeremy Thornton said the "gut-wrenching" flood was among the worst he had seen.

"It is pretty tough, we've had a few moments but you have to suck it up and push on," he told AFP.

"We are reliving it every second -- hearing the rain, hearing the helicopters, hearing the siren."

Kinne Ring, mayor of the flood-stricken farming town of Kempsey, said dozens of properties had been swamped.

"Houses have been inundated," she told national broadcaster ABC.

"There's water coming through the bottom of houses, it's really awful to see and the water is going to take a bit of time to recede."

Flash floods also threatened a wildlife sanctuary breeding endangered Tasmanian Devils, a meat-eating native marsupial.

"Our hardworking team has been out in tough conditions, moving animals to safety and getting food to where it's needed most," the Aussie Ark sanctuary said in a statement.

On the coast, people spotted dead cows washing up after rivers swept them from their pastures.

- 'Compelling evidence' -

From the arid outback to the tropical coast, swaths of Australia have recently been pummelled by wild weather.

The oceans surrounding Australia have been "abnormally warm" in recent months, according to Australia's government weather bureau.

Warmer seas evaporate more moisture into the atmosphere, which can eventually lead to more intense rains.

Although difficult to link to specific disasters, climate change is already fuelling more extreme weather patterns, scientists warn.

Flood modelling expert Mahdi Sedighkia said this week's emergency offered "compelling evidence" of how climate change could affect regional weather patterns.