NSW on flood alert as 7000 isolated

Major flood warnings have been issued for rivers across northern NSW as thousands remain isolated and Moree residents begin the "soul destroying" task of cleaning up.

About 90 per cent of Moree's residents returned home on Monday morning, after mass evacuations when flood waters inundated the town, cutting it in half.

Moree Mayor Katrina Humphries said the clean-up was vile, as temperatures hit 36 degrees.

"It's vile, it's soul-destroying," Ms Humphries told AAP, adding some people had lost everything.

"They were prepared but the water came higher in some parts of town.

Over 300 homes were deeply flooded and a similar number were less affected, she said.

The town's sewage system had fortunately held up, but some properties on the periphery of town which had independent septic systems hadn't been so lucky.

"You either have ... stuff gurgling up through your toilet and shower recess or (the tanks) split and everything goes everywhere," Ms Humphries said.

Evacuation orders have been lifted for Moree and its surrounds, with flood waters receding in Pallamallawa and Biniguy areas, the SES said on Monday afternoon.

"The long, hard recovery process has started," NSW SES Commissioner Murray Kear told AAP.

Meanwhile, in a wide area across the state, rural properties are isolated, with 7000 people cut off by floodwaters.

The worst affected area was south of Moree in Wee Waa where 2,300 people remained stranded, Mr Kear said.

"There have been some homes and businesses that have been inundated.

"Isolation is expected to continue for a further four or five days."

A major flood warning has been issued for the Namoi River at Wee Waa, with a moderate flood warning issued downstream for Boggabri and Narrabri.

At Narrabri the Namoi peaked near 6.6 metres around 4am (AEDT) on Monday, with moderate flooding, and it's expected to peak at Wee Waa this evening.

In a bid to help those impacted by the floods, the federal government has announced additional disaster assistance for communities in northern NSW.

Residents in Moree, Narrabri and Gwydir could be entitled to the Australian Government Disaster Recovery Payment (AGDRP), which will be made available through Centrelink.

The AGDRP is a one-off payment of $1000 per adult and $400 per child.

NSW Premier Barry O'Farrell has also called for support from the federal government to make Category C disaster declarations for northwest NSW, to allow eligible farmers and small business owners access to cash grants.

"The devastation I saw on Friday across parts of North Western NSW is so severe it's vital all governments provide local communities with the means to recover," Mr O'Farrell said in a statement.

"I have decided that Category C assistance is needed for Moree, Gwydir and Narrabri."

Governor-General Quentin Bryce and Michael Bryce are expected to visit the Emergency Recovery Centre in Moree on Tuesday, the council's spokeswoman said.

Meanwhile, major flood warnings are also in place for the Birrie, Bokhara, Culgoa and Narran Rivers, with levels at St George in Queensland hitting 13.48 metres on Monday morning and rising throughout the day.

The Barwon Darling River system is also forecast to get hit with major flooding, with peaks expected at the border town of Mungindi around Wednesday.

Mr Kear said the SES and the weather bureau were now preparing for flood waters expected to move across the state over the coming month.

"We have got water moving from the western rivers and Queensland and into the Darling.

"It could take up to two months to hit Bourke and Walgett," he said.