NSW residents have been forced to flee their homes and are being warned to stay vigilant as rising waters are expected to flood parts of the South Coast at high tide later in the day.

The SES had 200 calls for help overnight and 300 people have been ordered to evacuate their homes at Sussex Inlet and St George's Basin.

An aerial image of water flowing over the Jerrara Dam wall. Photo: Westpac Life Saver Rescue Helicopter

Some have taken shelter in an evacuation centre set up at a nearby bowls club, an SES spokesman said.

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Flooding is also expected in Nowra and may cause road closures and leave some properties isolated.

SES spokesman Phil Campbell said residents will probably be unlikely to return home, with high tide expected at 5pm.

Water flows over the edge of Jerrara Dam, west of Kiama. Photo: NSW SES Kiama Unit

The Bureau of Meteorology is warning of very heavy surf conditions and coastal erosion for parts of the Illawara and South Coast districts.

Meanwhile, attention remains on a dam that has begun eroding near Kiama.

Jerrara Dam showed signs of a failing wall on Tuesday morning, leaving 10 properties in serious risk and the nearby village of Minnamurra vulnerable.

Water flows over the edge of Jerrara Dam, west of Kiama. Photo: NSW SES Kiama Unit

The SES said 25 properties were evacuated on Tuesday night.

If the dam bursts it could cause dangerous flooding to areas including Mount Brandon Road, Jerrara Road and Jamberoo Road.

Rain is expected to ease by Wednesday afternoon.

AAP