NSW Premier Chris Minns is in the state's north ahead of the cyclone's expected landfall, which has prompted warnings for residents in several areas including parts of Lismore and Kyogle to evacuate by 9pm on Thursday.
The category two cyclone is expected to lash northern NSW and southeast Queensland with heavy rain and wind, forecast to peak late on Friday and early Saturday.
Lismore MP Janelle Saffin warned locals not to wait, after she and other residents had to flee in the middle of the night during devastating, sudden floods in 2022.
"It's hard to do it, but if you get an evacuation order, please do it," she said on Thursday.
"It's about 7000 homes across the region," she added.
Mr Minns advised people to try and seek shelter with family or friends to avoid overwhelming evacuation centres set up across the region.
Those remaining behind may not be able to be rescued.
"We cannot guarantee a boat for every house in the flood evacuation zone ... in the event of a major overflow of these rivers, particularly overnight," Mr Minns said.
"So the way to keep yourself and your family safe, particularly in the next few hours, is to evacuate before 9pm," he said.
The cyclone was initially forecast to dump rain for about two days, but its progress had stalled, and heavy falls could continue for longer.
"The window is now five days, which means there's major pressure on these communities," Mr Minns said.
Essential Energy has advised that 10,000 homes and businesses are without power due to heavy winds, and may remain disconnected for long periods of time.
Lismore Soup Kitchen chaplain Ian Phillips told AAP locals were anxious ahead of the storm.
"We're just gearing up for them to have a safe place to camp for as long as they need to ... there's a lot brewing for them because of their previous experience."Â
Acting SES chief superintendent Stuart Fisher said the cyclone could be worse than the 2022 floods.
Up to 700mm of rain could fall on the region with authorities advising residents "pray for the best but prepare for the worst".
More than 2000 emergency volunteers armed with drones, high-clearance vehicles and water pumps have been deployed but Mr Minns stressed they cannot be everywhere and urged common sense.
Fifteen evacuation centres have been established around the northern rivers region and more than 300,000 sandbags have been distributed.
SES Commissioner Mike Wassing said 20,000 people across 10,000 homes could be affected as "worst-case scenario numbers".
Federal and state disaster relief funds have been rolled out to communities in 15 local government areas in northern NSW, and on Lord Howe Island, to help cover immediate needs such as emergency accommodation.
Lismore Mayor Steve Krieg, who was an integral figure in the recovery and reconstruction of the city after the catastrophic floods, emphasised vigilance.
"We are at the very start of this weather event. It will be quite treacherous over the coming two or three days, so please stay safe and listen to the warnings," he said.
Cape Byron, the easternmost point of mainland Australia, will be in the eye of the storm with dangerous storm tides and destructive winds of up to 155 km/h predicted.
Intense rain could push rapid and dangerous river rises, the Bureau of Meteorology warned, with potentially major flooding along the Tweed, Wilsons, Bellinger, Brunswick, Nambucca, Richmond, Clarence, Orara, Macleay, Hastings and Camden Haven rivers.
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