Police found the body of a 63-year-old man inside a flooded home in the rural hamlet of Moto, about 400 kilometres (250 miles) northeast of Sydney.

Others clambered on to their roofs to escape the rising waters as authorities dispatched helicopters, boats and drones on a major search and rescue mission.

The storms have already dumped more than four months' of rain across parts of New South Wales in just two days.

"I must also say that we're bracing for more bad news in the next 24 hours. This natural disaster has been terrible for this community," state premier Chris Minns told reporters.

The town of Kempsey -- an agricultural hub on the banks of the Macleay River -- had been surrounded with little warning, mayor Kinne Ring told AFP.

"You often think of rain on tin roof as relaxing, but at the moment it is deafening and horrible," Ring said on Thursday.

"The downpours are torrential and every time it rains, you wonder what is going to happen next."

Ring said more than 20,000 people were isolated in her local government area alone, with many unable to access medication or supplies.

"This isn't a flood like we have seen in quite some time."

Minns said close to 50,000 people could be isolated by flooding across the Mid North Coast, where rivers flow off rugged hills to feed the verdant hinterland.

Authorities feared at least three people had gone missing.

- 'More natural disasters' -

From the arid outback to the tropical coast, swathes of Australia have been pummelled by wild weather in recent months.

The average sea surface temperature around the continent was the highest on record in 2024, according to the Australian National University.

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

"Unfortunately, we're getting better at deploying resources because of natural disasters," Minns said.

"And the reason for that is because we're seeing more of them, not less."

Some 2,500 emergency workers have been deployed to the region, Minns said, alongside rescue boats, a fleet of helicopters, and "hundreds" of search drones.

Emergency management minister Kristy McBain said rain continued to fall and some rivers were still yet to peak.

"We aren't over the worst of it yet," she told national broadcaster ABC.

Taree resident Holly Pillotto, who was among those briefly stranded on an upper level of her home.

"Our neighbours on the back verandah here are also stranded," she told Australia's Channel Nine as waters rose on Wednesday.

"It's a really dangerous spot to be."