A man who was swept down a swollen creek became the first casualty Sunday from floods inundating Australia's New South Wales state as hundreds more people were evacuated due to heavy rainfall.

Swathes of the state have been battling flooding for several days although the rainband that has dumped up to 200 millimetres (eight inches) of water was forecast to ease by Monday.

"People have been asked to leave their homes overnight as intense rainfall fell in southern and southeastern parts of the state," State Emergency Service commissioner Murray Kear told reporters.

"But just as we're standing under sunny skies (on the outskirts of Sydney), they will be under sunny skies tomorrow."

The body of a 43-year-old man was recovered after he and two friends became trapped when attempting to cross a creek late Saturday, police said.

When they tried to get out of the car they were washed away. One man was rescued as he clung to a tree and another was found further downstream suffering hypothermia.

Major highways and thousands of kilometres (miles) of local roads have been closed by floodwaters across New South Wales with the State Emergency Services carrying out 29 rescues overnight.

Heavy downpours continued to swamp the Riverina area in the state's south, causing major flooding, with hundreds more properties evacuated.

But there was better news for some 2,000 residents of the Hawkesbury-Nepean region on Sydney's semi-rural northwestern outskirts who were set to return home after evacuation orders were cancelled.

Salvation Army emergency services coordinator Norm Archer said he had rarely seen anything like it.

"The sheer size of these floods is something I haven't seen in NSW for many years," he said. "It's an enormous area that's affected."

The southern state of Victoria has also been hit by wild weather with record rainfall reported in some towns.

In Numerkah township in the state's north, a hospital and a care centre were both evacuated due to rising floodwaters.