NSW residents warned devastating flooding could continue for months

Residents in northern NSW dealing with their second floods crisis in weeks have been warned they could be hit by even more flooding in the coming months.

Acting Premier Paul Toole said today a wet forecast for April could lead to floodwaters rising once again.

"We may be in this situation, coming back again, in a few weeks' time," he said.

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"April is expected to be quite wet in many parts of the state."

With the ground already waterlogged from well-above-average rainfall to start the year, Mr Toole said it wouldn't take much more precipitation for rivers to break their banks.

"When you have a look at the ground, it is saturated," he said.

"We only have to see a small amount of rainfall landing in some of these areas...

"It doesn't take much rainfall to see those rivers running again, encroaching their banks, seeing riverine flooding, flash flooding within those communities."

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Mr Toole's warning came as Lismore experienced its second round of devastating flooding since late February, with waters breaching the town's levee and forcing the evacuation of the CBD this morning.

Flash flooding also hit Byron Bay after more than 400 millimetres of rain fell in parts of northern NSW.

The Bureau of Meteorology said yesterday the La Nina system which has been driving much of the rainfall has "slightly weakened" in the past fortnight and is due to finish by the end of autumn.

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However, it warned the system is still expected to influence weather over the next two months.

"La Niña events increase... the chances of above-average rainfall across large parts of eastern Australia during autumn," the BoM said in its climate driver update.