According to the Bureau of Meteorology (BOM), the Namoi River exceeded the major flood level of 7.90 metres during Saturday.

It peaked at 8.60 metres on Sunday morning, 40 centimetres higher than the major levels reached on Wednesday.

By Sunday afternoon, the river at Gunnedah was sitting at 8.58 metres, and the State Emergency Service (SES) described it as "steady".

Upstream of Gunnedah along the Mooki River, levels peaked at Breeza Station at 7.0 metres on Saturday, and had fallen to 5.24 metres on Sunday and continues to fall.

There's also major flooding at Narrabri and Wee Waa, where the river could remain at an extended peak for a week. Roads to the small town have been cut off by floodwater for days.

With the Gunnedah floods declared a natural disaster, emergency service volunteers have been run off their feet as homes in low lying areas of the town become inundated with water.

A flood evacuation centre has been established at the Gunnedah Basketball Stadium.

Out of town, residents have been cut off from supplies for up to a week, with the Rural Fire Service (RFS) aviation crews assisting the SES by undertaking flood rescues and delivering supplies.

On a property just outside of Gunnedah, Courtney Evans and her young family were cut off without access to food on Sunday when air crew from the RFS delivered vital supplies to the family and surrounding properties.

"I cannot thank the three men from the RFS for delivering much needed food to us today. Coles Gunnedah have also been amazing," she said.

The SES has urged more people to call-out for help if they need to stock up on food, emergency or medical supplies.

Incident Controller for NSW SES David Monk said supply drop offs for Gunnedah residents can be organised by calling 132 500, or 000 if the situation was life threatening.

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Gunnedah mayor Jamie Chaffey said his thoughts are with those who have had their homes, farms or businesses flooded, and those who remain isolated.

"Some people have now been isolated by flood waters for a week, with no certainty about when it will be safe to travel to stock up on supplies," he said.

"Added to the worries about supplies for the family and possible medical conditions are additional concerns about livestock and crops, with this flood coming at a terrible time for those who were about to harvest bumper crops.

"I want to assure people that you are not alone in this. There is help available, and we urge you to contact those who can offer assistance."

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