A woman is believed to be missing in floodwaters in Lismore, after the regional city had its levee breached for the second time in weeks.
The Wilsons River peaked above 10.65 metres on Wednesday, with floodwaters and mud spilling into the city centre.
A search operation is underway after emergency services were told a woman had become trapped in her vehicle in floodwaters at Monaltrie, south of Lismore, about 9.50pm on Tuesday.
Officers said they spent several hours looking for the woman and her vehicle but neither were found.
A multi-agency search is now underway, as Police Rescue, Water Police and the NSW SES hunt for the woman's white Holden Captiva station wagon.
Anybody with information is urged to contact police.
Dozens of people have been rescued in the past 24 hours, many of whom were attempting to drive through floodwaters, NSW SES Acting Commissioner Daniel Austin said on Wednesday.
The service received 902 calls for help and carried out 52 rescues in the past 24 hours.
Some 16,000 people have been told to leave their homes in NSW, with 13 evacuation orders active on Wednesday, seven issued as rain continued to fall during the morning.
"When you have a look at the rainfall, no one could have predicted some of the amounts we have seen," Acting Premier Paul Toole said.
Renewed flooding hit Lismore, Ballina, Byron, Coraki and Woodburn just as many people were returning to their homes and businesses after the previous floods.
Mr Toole said harsh, wet conditions were expected to continue, with a very wet April in prospect.
"We may be in this situation, coming back in a week's time," he said.
"When you have a look at the ground it is saturated."
Flood Recovery Minister Steph Cooke said the state had faced many natural disasters over recent years.
"Whether it's droughts or bushfires, and now floods," she said.
"We know this wet weather is likely to continue for quite some time, right throughout April and potentially beyond that.
"I know for many of you it must feel that this flooding emergency will never end, but I can assure you that there is light at the end of the tunnel."
Labor's spokesman for Emergency Services Jihad Dib said emergency services personnel were doing their best in a difficult situation, but the government needed to step up.
"It is beyond time for the government to take a lead role in co-ordinating the response," Mr Dib said.
"The mixed messaging about the river level falling while ... it was rising, only highlights the lack of co-ordination and single point of leadership required in an emergency."
He said it was not good enough that Byron and Lismore residents were still dealing with faulty water gauges and broken warning sirens a month after initial flooding.
Lismore Mayor Steve Krieg told AAP he had heard reports the Wilsons River had begun to tip over the top of the levee shortly before confirmation arrived from the Bureau of Meteorology on Wednesday morning.
"Everyone's exhausted. Evacuation orders started at four o'clock yesterday afternoon and then got cancelled before the phones started ringing again," he said.
"(People are) running on no sleep at the moment. It's hard to put into words. You're feeling angry as well because the messaging hasn't been what it should have been.
"The hardest thing for these people is they have spent weeks and weeks cleaning and getting rid of all the flood mud, sanitising and addressing the mould issue.
"Now you've got to virtually start all of that process from the start again."
Communities from Evans Head to Byron Bay were hit with 200mm to 300mm of rain within a few hours, causing significant and destructive flash flooding, BOM meteorologist Dean Narramore said on Wednesday.
Further south, Coffs Harbour, Dorrigo and Bellingen copped upto 300mm on Wednesday morning, while major flooding is occurring on the Bellinger River.
