More residents have been ordered to evacuate houses and caravan parks after forecasters predicted historic flooding for parts of NSW after days more of torrential rain.

Early on Friday, evacuation orders were issued for people living in Cornwallis and the eastern part of Richmond lowlands.

Residents in parts of Cattai, Pitt Town and Agnes Banks were also told to get out for fear of being trapped without power and water.

There are major flood warnings for rivers in the Hawkesbury-Nepean Valley and the NSW central and south coasts after deluges drenched the Sydney, Shoalhaven and Wollongong regions on Thursday.

Resilience NSW Commissioner Shane Fitzsimmons told Nine’s Today program on Friday that three evacuation centres had 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.

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Premier Dominic Perrottet told Sydney radio station 2GB the SES evacuations and warnings were saving lives.

“Despite the significant rain events we’ve had and the flooding, what’s been remarkable so far is how few lives we’ve actually lost and that’s because people are following those instructions,” Mr Perrottet said.

Emergency Services Minister Steph Cooke told 2GB she appreciated people heeding the advice.

“We’re constantly seeing rain of course, we’ve got flooding occurring … the interruptions to normal life are exhausting … but we will get through it and the SES are doing an amazing job of keeping people safe.”

She said the extent of flooding in the Hawkesbury-Nepean area would depend on how much further rain fell on Friday.

Mr Perrottet and Ms Cooke will give a further update later on Friday.

Earlier, the downpours and threat of flooding forced residents to evacuate in several areas, and some schools to close.

A total 24 schools would be closed on Friday, the NSW Department of Education said, with another 13 teaching classes at different sites.

Schools closed include Kurnell Public School in the Sutherland Shire, Camden High School in south-west Sydney, Fairy Meadow Public School in the Wollongong area, and Mount Kembla Public School in the Illawarra.

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On Thursday, evacuation orders were issued for residents in Camden and Chipping Norton in Sydney’s south-west and Woronora, Bonnet Bay and Gronos Point on Thursday, as flood waters began to rise.

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.

Warnings for possible evacuation were also in place for Stuarts Point on the mid-north coast, Stonequarry Creek, Picton and parts of Camden and Elderslie Sydney’s southwest, and Wallacia Weir in the Blue Mountains.

Major flooding is also occurring on the Nepean. 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 11.75 metres by 7am on Friday.

There is also major flooding at North Richmond on the Hawkesbury River. The Bureau of Meteorology believes the rises there will not be as severe as flooding that occurred last month.

Further downstream, the river exceeded last month’s height at Camden Weir, reaching 12.21 metres about 10pm on Thursday before falling back to 11.03 metres 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.

Water is also spilling over Warragamba Dam, which was at capacity when this week’s downpours started.

-with AAP