The weather system responsible for the flooding around Sydney was moving south on Monday into the south coast and into the East Gippsland region of Victoria.
It comes as heavy rain has been falling steadily across much of the state since Wednesday, with some of the strongest falls seen in northern NSW, near Byron Bay and Kingscliff, which had close to 300mm fall yesterday.
About 100,000 homes have also been left without power.
The heavy downpour began late last week. Rain is expected to continue until at least Thursday next week.
There are concerns the Georges River at Milperra could reach levels higher than 1988's flood.
Hazardous surf warnings are also in place for the Macquarie coast, Hunter coast, Sydney coast, Illawarra coast, Batemans coast and Eden coast.
Police divers are searching for a driver missing in Sydney's floods after his auto was washed off a causeway at Galston Gorge, in the city's north.
On Monday, the Bureau of Meteorology said that in the last four days, 391.6 mm of rain have fallen in the city, the most since February 1990 when 414.2 mm of rainfall were recorded, and warned of more rainfall in coming days, reports Efe news.
Emergency services have been swamped with calls since the deluge set in on Friday, while the extreme weather has caused transport chaos across Sydney.
In contrast, the authorities said that flood evacuation warnings have now been ordered for parts of the Conjola region, where deadly fires razed dozens of homes on New Year's Eve.
"And we are still seeing people driving into floodwater".
Tens of thousands of households in Sydney and the Central Coast were still without power on Tuesday night, with Ausgrid asking customers to prepare for outages into the weekend.
Many people have injured due to aftermaths of rain, including four men who were present in the auto that was crushed by a falling tree.
In the northern rivers region, a auto was washed off a road in Glenreagh, and in Tyagarah two people had to be rescued from a caravan due to rising floodwaters.
The State Emergency Service (SES) said there was major flooding up and down the coast and the main route from Sydney to Wollongong was closed in both directions.
"But we've surpassed those figures and you have to go back as far back as 1998 to see totals like we'll get", a weather bureau spokeswoman said.
Be aware that run-off from rainfall in fire affected areas may behave differently and be more rapid.
"I just hope that people have the wisdom and the foresight to realise that this should not be seen as a sign of not needing to act", he added.
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