Flood warnings are in place as a low-pressure system pushes torrential rain through the Northern Rivers and the mid-north coast of New South Wales.

The slow-moving low is sitting just off the Queensland border.

It has generated rainfall recordings of 50 to 70 millimetres near Lismore and Coffs Harbour overnight.

But the rain will intensify during the morning with falls likely of between 150 and 300 millimetres.

The weather bureau has issued a severe weather warning for people in the Northern Rivers, mid-north coast, the Hunter and Northern Tablelands.

Bob White, the local State Emergency Service (SES) controller in Coffs Harbour, says what worries local communities is that it is only three weeks since flooding rains last hit the region.

"The ground now is very, very wet, so any rainfall we do have is going to run off immediately," he said.

Coffs Harbour residents have already begun sandbagging local homes and businesses.

The SES has flood rescue crews and eight helicopters in the area.

Warnings for minor flooding are current for the Bellinger, Richmond, Wilson and Orara Rivers.