The NSW State Emergency Service (SES) said on Friday that flood incidents were mainly seen in the South Coast, Illawarra and Sydney metropolitan areas, Xinhua news agency reported.

The Australian Bureau of Meteorology (BOM) recorded 206 mm of rain in Cringilla, 197 mm in Port Kembla, 170 mm in Warilla and 146 mm in Wollongong in 24 hours, with wet catchments, full dams and increased risk of flooding. Very high tide.

NSW SES state duty commander and acting assistant commissioner Dallas Burns said rescue crews worked throughout the night in "very challenging conditions" in the state's south-east, while many roads may still be affected by flash flooding on Friday.

"This is a dynamic weather system where conditions can change rapidly," Burns warned.

Currently, flood warnings are in place for Picton, Shoalhaven, Wollondilly and Hawkesbury Nepean.

According to the BOM forecast, rainfall is expected to ease from Friday afternoon, with high river levels expected to fall over the weekend.