Residents have been ordered to evacuate houses and caravan parks after forecasters predicted historic flooding for parts of the state.
Evacuation orders were issued early on Friday for people in Cornwallis and the eastern part of Richmond lowlands as well as low-lying parts of Cattai, Pitt Town and Agnes Banks.
Residents in Camden and Chipping Norton in Sydney's southwest and Woronora, Bonnet Bay and Gronos Point were earlier ordered to evacuate as floodwaters began to rise on Thursday.
People were also warned to prepare for evacuation in parts of Ebenezer, Emu Plains, Mulgoa, Sackville North, Pitt Town Bottoms, Camden, Elderslie, Wallacia Weir and North Richmond for fear of being trapped without power and water.
Resilience NSW Commissioner Shane Fitzsimmons told Nine's Today program on Friday three evacuation centres have opened to support people who are facing another evacuation after already fleeing their homes several times in the past 18 months.
"This is really taking a toll with people right across NSW," Mr Fitzsimmons said.
The NSW education department has listed 154 schools, predominantly around Greater Sydney, the Illawarra and Shoalhaven regions that are not operating due to adverse weather conditions on Friday morning.
Major flood warnings are in place for rivers in the the Hawkesbury-Nepean Valley and the NSW Central and South Coast after torrential rain on Thursday.
Water is also spilling over Warragamba Dam, which was at capacity when the downpour started.
A major flood peak above levels seen during the April 1988 floods passed through Menangle on Thursday afternoon, where the Nepean River reached 16.83 metres on Thursday afternoon before falling back to 11.75m by 7am on Friday.
Further downstream, the river exceeded last month's height at Camden Weir, reaching 12.21m about 10pm on Thursday before falling back to 11.03m by Friday morning.
Wallacia is expected to experience a flooding at levels higher than last month when the Upper Nepean River peaks on Friday morning.
There is also major flooding at North Richmond on the Hawkesbury River, although the Bureau of Meteorology believes the rises will not be as severe as the flooding that occurred last month.
In Camden, numerous rescues were carried out on Thursday afternoon as the Nepean River burst its banks, with at least five people retrieved with State Emergency Service boats, footage aired on the Nine Network showed.
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