Wet weekend for Australia's eastern and northern coasts

Severe weather lashing Australia's east coast has led to warnings for hazardous surf and potential flash flooding, as the Top End braces for a brewing cyclone.

In NSW, sweltering heat has been replaced by heavy rain and damaging winds along the state's south coast and parts of the Illawarra, Southern Tablelands and Snowy Mountains.

On Saturday, the Bureau of Meteorology warned showers and isolated thunderstorms would bring heavy rainfall to parts of Greater Sydney.

The rain could lead to flash flooding with Penrith, Parramatta and Springwood potentially affected.

A hazardous surf warning was also in place for the Hunter, Sydney, Illawarra, Batemans and Eden coasts.

NSW Police urged people to consider staying out of the water and avoid walking near surf-exposed areas.

Rock fishers should avoid coastal rock platforms exposed to the ocean and seek a safe location sheltered from the surf, police said.

Damaging winds are expected for the mountainous areas around the Snowy Mountains and Southern Tablelands with strong east to south-easterly winds.

Meanwhile, clean-up efforts are under way in parts of Victoria after torrential rains quickly overfilled the Wye, Kennett and Cumberland rivers in holiday hotspots along the Great Ocean Road.

The extreme event carried huge amounts of water downstream, swamping campgrounds and upending vehicles.

Multiple cars remain stranded in the surf as authorities estimate some 10 to 20 vehicles to have been lost.

More than 178 millimetres of rain fell in the area in six hours, with the Lorne station registering its highest 24-hour rainfall since records began in 1884.

In the early hours of Saturday morning, the bureau issued an emergency warning for heavy rainfall in the western Top End, affecting people in Daly, Tiwi and parts of the Arnhem districts, brought on by a tropical low.

The warning said the rain could lead to flash flooding, with isolated falls of more than 140mm possible.

But there was uncertainty about where and when this rain would develop, with heavy rainfall more likely from Saturday afternoon into Sunday morning.

Communities are urged to stay updated on the latest warnings via the local State Emergency Service and weather bureau.