The SES says the Mehi River at Moree is expected to exceed 9.5 metres around 3pm today and peak around 10.3 metres by 9am tomorrow.

Residents are being advised to evacuate to south Moree where evacuation centres have been set up at the town hall and the PCYC centre.

Up to 260 residents at Croki and Manning Point have also been warned to prepare to evacuate as the Manning River continues to rise.

That evacuation order is likely to be put out later today.

The north has been hammered by 250mm of rain overnight, with the town of Wee Waa now completely isolated and about two and a half thousand residents there will be monitored through regular food and supply drops.

Barwon MP Kevin Humphries said as of 9am today evacuation warnings had been issued to 463 properties around Moree, 60 on the Wingham Peninsula, 40 in Taree and 19 in Barraba.

"Throughout the region we have seen close to 160mm of rain fall during the past two days to 6am this morning, with a lot more on the way today," Mr Humphries said.

"Unfortunately predictions are that this is going to be bigger than the floods that devastated the region in the 1970s."

The SES had been helping hundreds of residents prepare for evacuation.

The town of Moree is predicted to be split in half by floodwaters later today, NSW SES Deputy Commissioner of Operations Steven Pearce said.

"We think this is going to be bigger than the floods that occurred in the 1970s," he said.

"The town will be cut in two."

Severe downpours hit the town overnight, causing major flooding on the Mehi and Gwydir rivers.

Moree Plains Shire Mayor Katrina Humphries said the rain was relentless and was about to get "a whole lot tougher".

"We are only six weeks out from the last floods so the ground is sodden," Ms Humphries told ABC Radio today