The entire Lismore CBD is inundated after days of unrelenting torrential rain and the Bureau of Meteorology says the Wilson River could peak at 13.5 metres on Monday night, meaning the city is facing its worst flooding in nearly 50 years.
"Flood levels are expected to exceed those seen in 2017 and may reach the 1974 flood level," the BoM says.
A severe weather warning has been issued for the Northern Rivers and parts of the Mid North Coast and Northern Tablelands.
There is flooding across the region, many roads are cut and the State Emergency Service is warning people to heed warnings and avoid entering floodwaters.
The BoM is warning of the potential for life-threatening flash flooding with six-hourly rainfall totals between 80 and 120mm likely, possibly reaching in excess of 150mm.
The Richmond River is causing major flooding at Kyogle, Coraki and Bungawalbyn, moderate flooding at Woodburn, and minor flooding at Wiangaree and Casino.
South Murwillumbah has also been evacuated as roads are cut and the only way out is by boat.
The SES ordered the town of Mullumbimby to evacuate on Monday morning as the area is threatened by rapidly rising floodwaters from the Brunswick River.
Fire and Rescue and the State Emergency Service have been door knocking to ensure people evacuate.
Police will resume a search for a man who went missing in floodwaters in Lismore on Sunday.
Officers heard him calling out for help about 4pm but "lost sight of the man a short time later".
SES volunteers had carried out 70 flood rescues since torrential rain began falling on Tuesday, Premier Dominic Perrottet told reporters on Sunday.
"We know that whilst there might be blue skies in certain parts of NSW that does not mean that there will not be significant flooding events that occur over the course of this week," he said.
One NSW life has already been lost, with a man killed when his LandCruiser was carried away by floodwaters on the Central Coast, north of Sydney, on Friday.
