The premier was heartened by the response to his visit to the southern border town of Moama on Wednesday, where volunteers and locals have built a 200,000-sandbag levy to hold out the surging Murray River.

"Mates, local community, people coming together to help every person through this difficult time ... really sums up what is great about the Australian spirit and great about our country," he said.

There are close to 100 flood warnings and 43 disaster-declared local government areas across NSW, as floodwaters slowly recede and the focus turns to the massive task of cleaning up.

While earlier speaking to reporters at the emergency operations centre in nearby nearby Deniliquin, the premier said the losses were heartbreaking.

"(Farmers) have gone through a bloody tough time for four years," he said.

"We've had droughts and now facing what would be a bumper harvest for many will be lost because of this flooding."

Many homes were also "severely damaged" and the restoration would be challenging.

"It's tough but everywhere I go ... I see a really strong sense of community, optimism, strength, and that's the Australian way," Mr Perrottet said.

He said he was moved by the number of volunteers from around the country who had come to help.

"That is the great spirit of Australia and .... that instils me with the hope and understanding and knowledge that we're going to get through it just like we got through everything else."

In Moama, Mr Perrottet said he had been in close contact with Victorian Premier Daniel Andrews to offer "whatever support he needed".

"To see federal, state and local government agencies .... all working together I believe puts us in a very strong position to deal with the challenges that are coming our way," he said.

Deputy Premier Paul Toole said the long-term consequences of the crisis were not yet clear.

"We probably won't know the full extent of it until the waters do recede and we actually see whether or not farmers can get onto their paddocks and actually make any use of the harvesting that's available to them."

While conditions were easing, Flood Recovery Minister Steph Cooke warned her department was watching a weather system expected to cross the state on the weekend.

"As soon as floodwaters do recede, then we will be able to get in and do those rapid damage assessments and look to get communities back on their feet as quickly as possible," she said.

A severe thunderstorm warning was issued for the south coast on Wednesday, as convergent winds triggered dangerous cells around Eden and Merimbula.

The storms were capable of bringing heavy rain, flash flooding and damaging winds by evening.

The Bureau of Meteorology also expects possibly severe thunderstorms to develop across eastern NSW on Thursday.

Falls will persist on the coast into Friday before warmer and drier conditions develop into the weekend, BOM's Jonathan How said.

Meanwhile, thousands of residents remain under evacuation orders in Moree in far northern NSW, where the premier stopped by on Tuesday.

Although the water is subsiding, the town remains inundated after the Mehi River reached major flood levels.

A cleanup has begun with people pulling rubbish from waterlogged homes.

Major flooding continues in multiple towns including Echuca, Moama, Barham and Kerang on the NSW-Victoria border, Moree, Gunnedah and Narrabri to the north, and Hillston, Hay and Condobolin in the west.

Australian Associated Press