SYDNEY: Heavy rain triggered flash floods that cut off some inland towns in Australia's southeast on Monday, with fresh evacuation warnings issued for thousands of rural residents.

The country's fourth major flooding this year saw wild weather pummel parts of southwest New South Wales (NSW) and northeast Victoria overnight, bursting river banks and piling on more pain for flood-weary residents.

Prime Minister Anthony Albanese said on Twitter the flash flooding was "creating dangerous conditions" and that the federal government was working closely with the states on rescue efforts.

In rural NSW, roads, bridges and farms were submerged.

Molong, about 300 km (186 miles) northwest of Sydney and home to more than 2,000, was one of the towns hit by heavy flooding. Footage on social media showed a shipping container and household items floating down the town centre.

"Almost every shop went under," Mayor Kevin Beatty told radio station 2GB. He said what appeared to be a shipping container or a caravan was stuck on the highway near the town, making it harder for emergency crews to reach Molong.

Residents in Eugowra, population 800, have been ordered to move to higher ground after officials deemed an evacuation would be unsafe due to flash flooding.

Australia's east coast is suffering from a rare third straight year of the La Nina weather phenomenon which is associated with increased rainfall.

There are currently more than 100 flood warnings in place across NSW and 84 in Victoria after weather bureau data showed some areas received more than a month's worth of rain over 24 hours.

"We've seen a lot of flash flooding where streets have been awash. We've had water then entering homes ... ankle-deep water in some places," Victoria state emergency operations chief Tim Wiebusch told ABC television.

Heavy rain and thunderstorms also lashed the state of South Australia over the weekend. Dozens of schools have been forced to close there, while thousands of homes are still without power.