Forbes in the NSW central west is bracing for the overflowing Lachlan River to rise to a possible peak of 10.8 metres on Saturday, a high-water mark not reached since 1952.
Ashley Sullivan, from the State Emergency Service, said the water was already close to reaching the expected peak on Saturday morning and about 500 homes in Forbes were under evacuation orders.
The service received 213 calls for assistance and performed 10 flood rescues, including several in Forbes, he told ABC TV on Saturday.
"This is a very widespread and very prolonged flooding incident that we're planning for many, many more weeks and months of flooding and emergency response (for)," Mr Sullivan said.
The call-outs included a request on Friday to help a pregnant woman whose waters had broken.
SES volunteer Ryan Jones, who performed the rescue, said the woman was cut off by floodwaters in north Forbes and she needed help crossing the inundated roads to get to hospital with her midwife.
"The water was too deep and dangerous for private vehicles, so the only way for us to access this patient was via use of our high-clearance vehicles," he said.
Another person was rescued from their car after being trapped by rising waters near the centre of town.
Forbes Shire Council reported north Forbes had been cut off from the town's centre and south after multiple roads were closed.
About 1000 people were told to leave for higher ground despite minimal chance of weekend rain.
NSW Premier Dominic Perrottet said 50 Australian Defence Force personnel would be deployed in Forbes and about 200 troops would be made available for flooded communities across the state.
Major rivers across western and southern NSW were flooding, including the Murrumbidgee at Wagga Wagga, the Murray at Moama and the Lachlan.
Lightning Ridge, Collarenebri and Walgett in the state's northwest were all isolated by floodwaters.
Water levels at Wagga Wagga, the largest inland town in NSW, peaked at 9.72 metres on Friday, the highest in more than a decade.
The SES has repeatedly warned people in inland areas of the dangers from so-called "blue-sky floods", during which rivers can rise to high levels despite rain no longer falling.
The agency had responded to nearly 2500 requests for assistance and performed 114 flood rescues during the past week.
More than 2660 buildings have been assessed with 1147 damaged.
Meanwhile, police divers continue to search for the second of two men swept out of a ute tray into a flooded river in the state's Southern Tablelands region on Monday night.
The other man's body was found on Thursday afternoon.
Across the border in Victoria, more than 40 flood hazard warnings were active on Saturday morning and hundreds of roads remained closed.
Major flood warnings were in place for the Murray and Edward Rivers, including for the highest flood peaks in around 50 years at Barham, Wakool Junction, Boundary Bend, Euston, Mildura and Wentworth.
Water levels at Mildura are expected to continue rising throughout November before a possible high in December.
Along the Murray River at Echuca and Moama, major flooding was expected to continue into next week although water levels were falling.
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