Thousands of people have been evacuated across NSW as swollen rivers flood towns, but the worst is potentially yet to come, the government says.
There are 40 flood warnings and 20 evacuation orders in place running from the Mid-North Coast down to the Illawarra, including western Sydney, with more expected to be declared on Monday.
NSW Premier Gladys Berejiklian plans to observe the flooding from the air on Monday.
"We're not through the worst of it potentially and that's why we need to brace ourselves," she told reporters.
"We have no illusions about how difficult the next few weeks and months will be."
Major flooding is still expected along the Macleay River at Kempsey and Smithtown on Monday.
People in Kempsey's CBD were told by the State Emergency Service to evacuate by midnight with the town levees due to be topped.
Evacuation orders are also in place for low lying areas of Macksville, Port Macquarie, the lower Macleay, Wauchope and Rawdon Island, Taree and Wingham.
In Sydney, parts of Penrith and other areas along the Nepean were ordered to evacuate on Sunday.
A number of towns across the state have been isolated for days, some without fresh water or power.
Roads have been cut off, hundreds of homes are inundated and 200 schools shut.
Heavy rain will remain a serious risk for the Mid-North Coast on Monday and Tuesday, where communities are facing the worst flooding conditions since 1929.
Communities along the Hawkesbury River are also bracing for the worst flooding in the area since 1961, with the river predicted to reach a peak of up to 15 metres on Monday night.
The Warragamba Dam has spilled over, and floodwaters are set to inundate places such as Windsor, Pitt Town, North Richmond, Freemans Reach and Colo.
"Extensive outages of water, electricity, sewerage, telecommunications and gas are expected to last many weeks or months," the NSW SES said.
The Northern Rivers, Hunter and Central Tablelands districts also need to be on high alert, the Bureau of Meteorology warned.
People are being asked to move possessions up high, take pets, essential items, warm clothes, medicines, insurance documents and valuables with them and stay with family or friends, or head to evacuation centres.
The SES is warning the deluge will continue and more evacuations are likely.
It is a miracle no lives have been lost, Ms Berejiklian said.
"I'm so relieved."
"I don't want to jinx it, but until this point in time, no one has lost their lives which is pretty much a miracle given what we've been through."
"The priority right here and now is getting people out safely from their homes and saving as many people ... and property as much as possible," the premier said.
Already 2800 residents had been evacuated but this could escalate to 54,000 if weather bureau predictions eventuate.
The good news is that flooding is easing on the Nepean River and in some parts of the Mid-North Coast region, and some evacuees can return home, the premier said.
Those evacuated from the western part of Jamistown and Penrith, and the northern end of Mulgoa are among those given the all-clear to return home.
Prime Minister Scott Morrison said while NSW had not yet made a formal request, he expected the Australian Defence Force would be deployed to help with the recovery.
"These are very, very serious storms and floods," he told Sydney radio 2GB.
