Further rain may hit the NSW coast as people living in already saturated catchment areas prepare for more water to flow to flood-stricken communities.
Showers and storms could develop on the east coast on Sunday evening, the Bureau of Meteorology says, although inland areas that have received the bulk of recent rainfall are expected to be spared.
But another storm system is forecast to develop over central Australia on Tuesday, bringing widespread rain and thunderstorms to eastern states by mid-next week.
Residents in parts of Narrandera, on the Murrumbidgee River in the Riverina region, have been told to leave due to moderate flooding and warned they may become isolated if they remain beyond 6pm on Sunday.
The river's main flood peak has passed Wagga Wagga but is expected to deliver moderate flooding downstream at Darlington Point from Thursday.
The Murrumbidgee has passed the minor flood level at Balranald while major flooding is not expected to reach the town of Hay until late October, the BOM says.
People in tourist and caravan parks at Moama, on the Victorian border, have been told to evacuate by 9am Monday.
Heavy downpours in Victoria are expected to affect towns along the Murray River, including Moama, from midweek.
Flooding there is likely to be as bad or worse than the 1993 flood, the area's second-biggest on record.
To the northeast, Cummeragunja residents have been told to evacuate as the Murray threatens to cut off routes to safety by noon on Monday.
Major flood warnings are in place for 11 rivers in NSW, with renewed flooding possible in some areas despite a temporary let-up in the rain.
Thousands of residents in Forbes, in the state's central west, have been affected after the Lachlan River peaked on Friday night.
Major flooding at Warren is expected to continue and more rain could cause further rises on the Macquarie River, threatening more severe flooding at Wellington and Narromine in the coming days.
October rainfall records have been set in parts of inland NSW, including at Broken Hill in the state's far west.
Sydney has also recorded its wettest year on record after only 10 months.
Prime Minister Anthony Albanese announced on Sunday four more areas were eligible to apply for federal financial assistance.
The addition of the Central Coast, Coonamble, Goulburn-Mulwaree and Parkes bring the total number of NSW local government areas with assistance available to 31.
"It's heartbreaking to think that for many people this is the third or fourth time in 18 months that their lives have been disrupted by a natural disaster of this magnitude," Mr Albanese said.
Almost 400,000 residents live in the four newly added LGAs, however close to 350,000 of them are on the Central Coast, and not all have been directly affected.
Support payments also became available in 40 LGAs across Victoria and Tasmania on Sunday.
