Houses have been “washed away” in surging floodwaters as the intensifying crisis in NSW triggered “one of the biggest operations” in the state’s history.

Residents of Eugowra in the central west said a sudden flash flood left people desperately clinging to roofs.

They described two enormous surges of water rushing through town from the swollen Mandagery Creek, even inundating homes built on stilts.

“It’s almost like a tidal wave hit town,” local Therese Welsh told AAP.

“There was just so much rain.”

“There’s so much destruction — homes have just been washed away.”

Mrs Welsh said the deluge had nowhere to go due to the already flooded Lachlan River.

“It was like the water had waves. That’s how fast it was running.”

The State Emergency Service said 150 people were plucked to safety from rooftops in Eugowra and Molong on Monday, with 11 helicopters flying them to Orange.

Further west, in Forbes, the town is bracing for its worst flooding in 70 years, with the Lachlan River expected to reach the 10.80m flood record of 1952 on Tuesday afternoon.

The Bureau of Meteorology said even further rises were possible depending on dam outflows and upstream peaks.

The Wyangala dam is spilling at record levels, with 230,000 megalitres being released a day, exacerbating flooding along the Lachlan River.

Weatherzone said the area had seen colossal rainfall — the highest in 147 years in Forbes.

Forbes collected 118mm of rain in the 24 hours to 9am on Monday, which was its heaviest daily rainfall in records dating back to 1875.

Further east, Canowindra’s 120mm over the same period was its highest daily total since 1956.

The sudden influx of water caused river levels to rise rapidly and exacerbated major flooding along the Lachlan River.

Just two weeks after Forbes had already flooded, about 1000 people were told to evacuate again and some 500 to 600 homes and businesses were expected to be inundated.

‘Battered and bruised’

“Our communities in the central-west have been battered and bruised and they are in the firing line again,” NSW Premier Dominic Perrottet said on Tuesday.

He said rescue efforts were focused on the central-western NSW towns of Eugowra and Forbes, where 14 aircraft have been used to help stranded residents.

“We know for many of our communities in the central-west, there is a lot of pain and a lot of hurt. But we’ve got through these challenges in the past and we’ll get through these challenges again,” he said.

“We do expect a difficult period of time over the next couple of days.”

Tweet from @NSWSES

Biggest operation in state’s history

About 100 Australian Defence personnel have been deployed to help in rescue operations, with 12 New Zealand volunteers arriving on Tuesday.

A further four aircraft are helping with logistics and transport, including flying food and other supplies into isolated communities.

Mr Perrottet said he had spoken to Deputy Prime Minister Richard Marles about more assistance from the Australian Defence Force.

“We’ll have more boots on the ground today, with an additional 180 defence personnel,” he said.

SES Commissioner Carlene York described the response “as one of the biggest operations … across NSW in its history”.

The Bureau of Meteorology’s Steven Bernasconi said there were 17 flood warnings across NSW, eight major ones affecting 25 locations.

Outlined major flooding at Forbes is expected to peak at levels similar to 1952. Cowra is expected to see a 14.3-metre peak, Namoi could reach 13.6 metres and Condoblin at 7.4 metres.

Communities at Collarenebri, Lightning Ridge, Tilpa, and Weilmoringle remain isolated.

Brewarrina can still be accessed by trucks.

There is also major flooding at Bathurst, where the river peaked at 6.4 metres but has since fallen significantly and Eugowra, which peaked at nine metres and is slowly falling.

Tuesday’s evacuation order for Forbes came just over a week after it experienced record flooding that damaged homes, businesses and roads.

The latest flooding crisis across NSW has stretched over 63 days with 70 local government areas falling under a natural disaster declaration, Emergency Services Minister Steph Cooke said.

On the 63rd day of the flood crisis Ms Cooke spoke of the ongoing devastation, saying Condobolin was entirely isolated.

“This just isn’t people’s houses. These are people’s homes. It’s their belongings, it’s their memories, it’s their livelihoods and it’s their futures,” said in Sydney.

Elsewhere, the Wyangala dam is spilling at record levels, with 230,000 megalitres being released a day, exacerbating flooding along the Lachlan River.

Mr Perrottet said his government was committed to raising the dam, saying it would protect lives.

About 150 people were rescued on Monday from roofs in Eugowra and nearby Molong, with extensive damage in the historic town.

SES Chief Superintendent Dallas Burnes said people in Eugowra were shocked at how quickly the water level had risen.

“The velocity was extremely fast – too fast in many cases to put boats in the water. Hence the evacuations we performed yesterday with the 12 assets we had on hand via helicopter,” he told Nine’s Today Show.

The SES had performed 222 flood rescues and received 909 requests for help in the 24 hours to Tuesday morning.

A cold front will move to the south on Tuesday. Snow is expected in southern parts of NSW before a high-pressure system from the south leads to conditions clearing on Wednesday.

-with AAP