Two missing in flood-hit NSW town

A multi-agency search is underway for a man and a woman believed missing during severe flooding in the NSW central west town of Eugowra, as the entire region remains on high alert for renewed inundation.

Rapid torrents of water reached roof height throughout the town early on Monday morning, destroying roads and infrastructure and taking many locals by surprise.

Dianne Smith, 60, was last heard from on Monday morning when she called a relative from her car in the historic town as it went under.

When unable to make contact with her, her relatives contacted police.

Also believed to be missing is Ljubisa "Les" Vugec, 85, who was last seen at his home in Eugowra about 9am on Monday.

Searches are now underway in the Eugowra area for the missing pair, involving numerous police agencies and the State Emergency Service.

Premier Dominic Perrottet said wider rescue efforts were now focused on 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."

An evacuation warning was issued for Forbes on Tuesday morning, saying the Lachlan River was rising faster than anticipated and about 1000 people in the town needed to leave immediately or risk being cut off.

With river levels rising faster than expected, about 500 to 600 homes and businesses are anticipated to be inundated again under the gushing water.

On the 63rd day of the flood crisis Emergency Services Minister Steph 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," she told reporters in Sydney.

About 100 Australian Defence Force personnel have been deployed to help rescue operations, with 12 New Zealand volunteers arriving, along with 14 aircraft supporting and rescuing residents and another four helping with logistics and transport.

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 17 flood warnings are in place with eight major alerts affecting 25 locations.

Major flooding is occurring at Bathurst where the river peaked at 6.4m but has fallen significantly and Eugowra, which peaked at 9m and is slowly falling.

Major flooding with an extended peak is also expected at Gunnedah and Wee Waa, west of Tamworth, from Tuesday into Wednesday. Both communities have been hit with repeated flooding in recent months.

The evacuation order for Forbes comes just over a week after it experienced record flooding that damaged homes, businesses and roads.

Forbes Mayor Phyllis Miller said people were shocked by another inundation.

"They can't believe this could happen twice in such a short period of time," she told ABC TV on Tuesday.

"This is really heartbreaking. Our farming community and businesses are suffering terribly."

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 because it will protect lives.

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.