Two young boys are missing in the fast-flowing floodwaters threatening the northern NSW town of Coonamble, emergency services say.
Reports of at least one child being swept into the Castlereagh River sparked the frantic search one kilometre south of the Coonamble bridge just after 5pm (AEDT) on Monday, a State Emergency Service (SES) spokesman said.
Police have since confirmed two young boys - aged seven and nine - are missing.
The local boys were part of a larger group who had been swimming near the northern side of the bridge.
"At the time, they had been swimming with three other children who have since been located safe and well," a police spokeswoman said.
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Emergency crews including police, ambulance and SES personnel are conducting an extensive search of the area using a helicopter and a number of boats, she said. A section of the riverbank has also been cordoned off.
SES spokesman Steve Delaney said he had heard anecdotal reports the children were "rejoicing" what they thought was the passing of the floodwater's peak.
However, news of the missing boys came as residents of the already-isolated township again faced rising floodwaters.
Hundreds of people from the eastern side of the township evacuated their homes on Sunday night and more people may be displaced as the Castlereagh River continues to swell. Expectations the waterway would reach its peak just after midday (AEDT) on Monday were revised, with the river now expected to hit its high point by 9pm.
"At 2.15pm (AEDT) the Castlereagh River at Coonamble was 5.17m, which is a slight rise since noon," the Bureau of Meteorology (BOM) said in a statement.
"Local SES reports indicate that at 2.30pm (AEDT) the Castlereagh flood peak was at Combara Bridge, which is approximately three hours upstream of Coonamble, so the final peak should arrive at Coonamble between 6 and 9pm."
That peak is forecast at 5.3 metres, edging Coonamble's ageing levee.
"It's only a minor rise compared to what we've already seen but it certainly puts a stop to a lot of things that we had hoped to do tonight, such as let people return to their homes," SES spokesman Steve Delaney told AAP.
Concerns the township's levee would rupture under the increasing water pressure have prompted constant monitoring by engineers.
"An engineer took a look at the levee this afternoon and said there are no serious concerns about the integrity of the levee up to 5.3m," Mr Delaney said.
Anything above that level is expected to challenge the levee. In anticipation of the peak, residents in the affected area, east of Coonamble, have again been issued an evacuation order.
"If we get that peak tonight, and we are happy that it is the peak that has gone through and there is nothing more behind it, we may be able to allow them (residents) back in," Mr Delaney said.
However, forecast severe thunderstorms for parts of NSW including Coonamble, late on Monday, pose another obstacle to plans for residents to return home.
The BOM has issued a warning for severe thunderstorms producing damaging winds, very heavy rainfall and flash flooding at Glen Innes, Inverell, Gunnedah, Narrabri, Coonabarabran and Coonamble.
Additional flood warnings remain in place for the MacIntyre, Peel, Namoi, Bogan, Culgoa, Bokhara, Narran, Warrego, Paroo and Barwon-Darling rivers.
"Flood warnings will remain on these rivers for weeks to come," Mr Delaney said. NSW Premier Kristina Keneally on Monday visited Coonamble, where she announced the flood-affected township and other regions would be formally recognised as natural disaster areas.
The local government areas of Bourke, Coonamble, Tamworth, Warrumbungle and Warren are now all disaster declared, meaning residents, primary producers and councils are eligible for financial assistance.
