Flood warnings in place amid heavy rainfall forecasts

Suburbs including Tamworth, Gunnedah, Narrabri, and Moree are forecast to receive up to 45mm of rain across the day, with isolated falls of up to 70mm.

Meanwhile, the Mid North Coast to the Hunter region is forecast to receive up to 80mm throughout the day, with isolated falls of up to 110mm.

"It's just light or moderate rainfall, but it's the prolonged nature of the rainfall this week, rather than how heavy it is, which is expected to cause flooding issues down the line," the Bureau of Meteorology's Angus Hines said.

Mr Hines warned that the worst of the wet weather and flood risk may be on Thursday with the ground set to be soaked from 24 hours of rain.

"Tomorrow's rainfall, as it gets a bit heavier, is likely to run directly into those rivers and we certainly expect to see river level rises," he said.

A flood watch spanning these regions has been issued warning residents of the potential of minor to moderate flooding late on Wednesday, with the possibility of major river level rises.

Flood warnings are already in place for the Namoi and Barwon Rivers as water levels are already high from rain a few weeks ago.

The Gwydir and Namoi Rivers in the state's northwest could reach major flood levels, while the Nambucca, Peel, Wollombi Brook, Lower Hunter and Colo Rivers may be at moderate levels.

Major flood levels are the highest warning to be issued for a river, with extensive inundation of land and potentially properties. 

Moderate levels mean the rivers have broken their banks and may be impacting infrastructure, including roads.

It follows extensive flooding in May in Taree that left homes destroyed and residents isolated for days, claiming five lives.

The Manning River exceeded a 1929 record during recent flooding in the town, peaking at almost 6.5m and bringing widespread devastation.

NSW SES is preparing for an increased number of calls for help across the multiple regions by deploying aircraft, high clearance vehicles and crews.

"While we're prepared for an increased volume of calls for assistance, we ask the community to prepare too," Assistant Commissioner Colin Malone said.

"Stay across the latest warnings and advice via the Hazards Near Me app and set up a watch zone for your local area."

There is also the potential for flash flooding during this rain event, with authorities repeating the warning to not drive through swamped roads.

"If you come across a flooded road, turn around and find another way," Mr Malone said.