Overnight, Tropical Cyclone Alfred was downgraded to a tropical low but millions of people in NSW and Queensland have been told to bunker down for dangerous conditions including flash flooding, heavy rain and intense winds.
Major flooding is expected at the Wilsons River, which runs through Lismore, where the river height is predicted to reach around 10.6m, the height of the levee.
In an update, the SES said the river was at 9.04m and rising, above the moderate flood level of 7.2m.
Saturday was "D-Day" for the weather event, NSW SES Commissioner Michael Wassing said.
"Irrespective of the crossing of the cyclone currently in Queensland, we're still seeing very strong winds," he said.
"But more importantly, we're still seeing very heavy rainfalls and therefore river rises, flash flooding and continued inundation of many areas."
NSW Premier Chris Minns said the next 24 hours would be crucially important as the weather system moved across the area.
"The message hasn't deviated, particularly as we move through to the flood part of this natural disaster," he said.
"That is, never drive through floodwaters, never put yourself in danger. It is the most common way of people losing their lives during these flooding events."
In the past 24 hours, there were 30 flood rescues, predominantly from people driving through floodwaters.
There are currently 131 warnings, including 40 emergency warnings, which equates to approximately 20,000 people under evacuation orders.
Mr Wassing said while levees had not overtopped, the SES was ready for all outcomes.
"The CBD levee and the levee to the south part of Lismore has not overtopped ... but we are getting flooding in low lying areas in Lismore," he said.
"Certainly with the Wilson River, the predictions indicate that there will be rises and there is likely to be further flooding."
With significant power outages affecting Lismore, leaving around 43,000 premises without power, Prime Minister Anthony Albanese said six generators were being sent from the national stockpile.
"Right now, very clearly, we need to stick together and continue to look after each other," he said.
"The impacts are already being felt and there is worse to come in the hours ahead."
Mr Albanese is expected to visit the region in coming days and urged people to remain vigilant and stay out of floodwaters.
"Please continue to stay up to date with the latest advice via the disaster The Disaster Queensland website, the NSW SES website, the Bureau of Meteorology website and through your local ABC Radio station," he said.
