SYDNEY: Fresh evacuation orders were issued for tens of thousands of Sydney residents on Monday after relentless rains flooded several suburbs, with officials warning of more wild weather to come.

An intense low-pressure system off Australia's east coast is forecast to bring heavy rain through Monday across New South Wales after several places in the state were hit with about a month's worth over the weekend.

Since Sunday, about 30,000 residents in New South Wales state have been told to either evacuate or warned they might receive evacuation orders.

Frustration swelled in several suburbs in the west of Australia's largest city after floods submerged homes, farms and bridges there, some for the third time this year.

"It's just devastating. We are in disbelief," Camden Mayor Theresa Fedeli said.

"Most of them have just come out of the last flood, getting their homes back in place, their businesses back in place and unfortunately we are saying it is happening again."

An operation was underway to rescue 21 crew members from a cargo ship, which lost power south of Sydney and risked being swept ashore, local media reported.

"It has been a very difficult time for many months to have this flood event off the back of others. It makes it more challenging," New South Wales Premier Dominic Perrottet said during a televised media briefing.

Paul O'Neill, a resident from flood-hit Wisemans Ferry, said he was taking food supplies by boat to his stranded family after rising waters cut off access.

"The road collapsed and hasn't been fixed since the last floods, hasn't been touched. So now they close our road access and then the ferry, the only way to get home now is by boat," O'Neill told Reuters.

AUSTRALIA 'UNDER-PREPARED'

Footage on social media showed petrol stations, homes, cars and street signs partially under water while garbage bins floated down flooded roads. Military vehicles were seen going into flooded streets to evacuate stranded families.

Some inland towns, including Picton, about 90 km (56 miles) southwest of Sydney, have lined the main streets with sandbags.

About 100 millimetres (4 inches) of rain could fall in the next 24 hours over a swath of more than 300km (186 miles) along the New South Wales coast from Newcastle to the south of Sydney, the Bureau of Meteorology said.

"We are expecting the rain to pick up again from this afternoon," bureau meteorologist Jonathan How said.

More than 200mm of rain have fallen over many areas, with some hit by as much as 350mm since Saturday.

The weather could trigger flash floods and landslides, with river catchments already near full capacity after the La Nina phenomenon, typically associated with increased rainfall, lashed Australia's east coast over the last two years.

Climate change is widely believed to be a contributing factor to the frequent severe weather events, the Climate Council said, adding Australia is "under-prepared".

Federal emergency management minister Murray Watt said climate change must be taken "seriously" due to the frequent occurrence of floods.

"The reality is we are living in a changing climate," Watt told ABC television.

Bad weather has delayed by 24 hours Monday's scheduled launch of a NASA rocket from the Arnhem Space Centre in north Australia, operator Equatorial Launch Australia said.

(Reporting by Renju Jose and Jill Gralow; Editing by Sam Holmes, Lincoln Feast and Edwina Gibbs)