Water is lapping behind shops in Forbes as stressed locals wait for the worst flooding in the central west NSW town in 70 years.
Emergency services have 22 emergency evacuation warnings out across the state including for Wagga Wagga, Gunnedah and Moama.
Some evacuations have been in place for more than two weeks.
Premier Dominic Perrottet visited Forbes on Friday where the overflowing Lachlan River could by evening exceed 10.8 metres, a mark not reached since 1952.
About 1000 people have been told to leave for higher ground.
"Follow those evacuation orders, even if you don't see flooding around you," Mr Perrottet said.
"That's the best way to keep you and your family safe."
He said 50 Australian Defence Force personnel will be deployed in Forbes, with about 200 available for flooded communities around NSW.
SES senior manager Ashley Sullivan said the ADF is helping with night-time rescue capability, and support is on the way to communities in preparation of significant expected flooding.
"The ground that we're standing on here will be inundated later today," Mr Sullivan said from Forbes, where floodwaters could be seen behind him.
Emergency Services Minister Steph Cooke said residents in some communities might not see their property directly affected but could be isolated due to flooding, the most recent of which has eclipsed other events earlier this year.
"We are now seeing flood upon flood upon flood, the layering of one flood on another," she said.
Forbes Shire Council mayor Phyllis Miller earlier told ABC Radio floodwaters were "lapping on the back streets of the shops".
"It's pretty awful but it's what we've expected," she said.
The flood peak about 20 kilometres upstream of Forbes on Friday morning was expected to reach the township by evening, the Bureau of Meteorology said.
Emergency accommodation has been set up at a local school.
Local cattle farmer Charles Laverty spent Thursday sandbagging his property on the outskirts of Forbes, with about one third of his paddocks already underwater.
Continued flooding has hit the area and other farming communities hard, as they struggle to recover from repeated bouts of destruction to crops and livestock losses.
"A lot of (my neighbours) have given up on harvesting those areas, which is very expensive," Mr Laverty told AAP.
"The losses are going to be devastating for them."
With livestock losses mounting in Forbes, the NSW Department of Primary Industries has stepped in with local agencies to airlift some 1200 sheep via helicopter.
The rescue operation, using a cage suspended underneath, took about eight hours to move all the animals to a safe location on higher ground.
Meanwhile, police divers continue to search for a man swept out of a ute tray into a flooded river in the Southern Tablelands.
Two men were flung from the tray on Monday night when the ute was driven across a causeway. The other man's body was found on Thursday afternoon.
Elsewhere, the Murrumbidgee River has caused major flooding and evacuation orders at Wagga Wagga.
The river reached 9.72 metres on Friday morning, above the December 2010 mark and on its way to a 1952 record by the evening.
Major flooding at Hay is expected to worsen from mid-November while moderate flooding is occurring at Tumut and Narrandera.
In the west, flood peaks are flowing into the Barwon-Darling River system, causing flooding at Mungindi, Mogil Mogil and Walgett.
Brewarrina, Bourke and Louth are among towns warned to prepare for major flooding, similar to that experienced in September 1998.