NSW State Emergency Services commissioner Carlene York declares response to flood emergency in western NSW biggest in state's history

Canowindra, Molong and Eugowra were the state's major areas of concern on Monday following the deluge of rain, with many parts of the west receiving over 100 millimetres in the space of a few hours.

In total, the NSW SES received over 900 requests for assistance and there were 222 flood rescues.

The bulk of those were in Eugowra, where there were 159 flood rescues from 180 calls for assistance. The population of the small Cabonne town on the banks of the Mandagery Creek is 770 people.

Commissioner York said the SES is now leading the biggest flood response operation in the state's history and the main areas of focus at lunchtime Tuesday remained Eugowra and Forbes.

She said there's a number of creeks and rivers currently flowing into the Lachlan, which will then flow through Forbes and go on to impact a number of communities further down stream too.

She said water "rose much quicker than expected" in Eugowra on Monday. The river heights doubled overnight from Sunday at 9pm to 8.15am Monday morning, peaking at 9.75 metres in Eugowra.

She said many of the 159 flood rescues in Eugowra were people on roofs of homes and businesses.

There were 14 helicopters in operation throughout the day, many of which flew between Orange and Eugowra to both bring people to safety and refuel.

Those helicopters were from the SES, Rural Fire Service, Australian Defence Force, NSW Police, NSW Ambulance and the NSW Royal Life Saving Club.

Commissioner York said rapid damage assessments are being conducted in Eugowra at the moment, with more ADF boots on the ground in town and an influx of help from across the ditch too.

Twelve emergency service personnel from New Zealand have flown into Australia to assist the efforts across NSW.

The group will be based in Parkes and deployed as mobile resources around the region as needed.

It is the first time the NSW SES has brought in international help.

NSW Premier Dom Perrottet said the "challenging period" the Central West has landed in still has many difficult days ahead, with more storms predicted for the weekend.

He recognised communities - particularly in Molong, Eugowra, Canowindra and now Forbes, again - were "bruised and hurting", but said it was all hands on deck to ensure the safety of everyone in the firing line.

Evacuation orders for Forbes affect 1000s of businesses and homes on Tuesday.

The floodwaters are rising fast, Minister for Emergency Services and Resilience Steph Cooke said.

"At the moment we're expecting 500 to 600 homes to experience inundation in Forbes," Ms Cooke said.

"We're anticipating similar river levels - 10.8m, 10.88m - in the days ahead. Similar to those two weeks ago.

"It's devastating for Forbes community."

There's 70 Local Government Areas across NSW that have been declared a natural disaster, and that event is now in its 63rd day, such has been the magnitude of this La Nina period and rain event.

Mr Perrottet said the NSW Government would provide more assistance for those communities hit hardest by the flooding.

"To the community in Forbes, we're with you every step of the way. It's been flood event after flood event after flood event," he said.

"The orders in place are there to keep families safe.

"Many communities in the Central West are in pain and hurting, but we've gotten through challenges in the past and we will again."

Mr Perrottet said the response to the situation unfolding in the region would encompass all three levels of government.

He's spoken to with acting Prime Minister Richard Marles - Anthony Albanese is at the G20 Summit in Bali - and has been handed additional ADF support. There will be another 100 ADF personnel flown in to assist the region in recovery.

"We will get communities back up on their feet as quickly as possible," Mr Perrottet said.

But the Premier warned the worst of the situation may be to come.

He urged the region, with more rain predicted throughout the week, to not take any chances in floodwaters. There's a 90 per cent chance of more rain in Orange on Sunday. While the forecast for Forbes, according to the Bureau of Meteorology, is an 80 per cent chance of rain on Sunday.

"We need to make sure as we go through this period with the ground being so wet, it's not taking much rain at all for flooding to occur; don't drive through floodwaters," he said.

"We lose lives when people drive through floodwaters. You're putting you and your family at risk, as well as our emergency services personnel."