Flood fears prompt evacuation calls in Sydney

Predicted major flooding has sparked evacuation calls as rivers continue to rise following days of heavy rain in parts of New South Wales.

Heavy falls bucketed on Sydney and surrounding areas as a surface trough lingered over the coast to close the week.

While the rain is expected to ease on Saturday, flood risks remain after the dam supplying 80 percent of the city's drinking water began to spill, posing downstream flooding threats.

The SES conducted 13 flood rescues in the 24 hours to 5am on Saturday, responding to close to 300 incidents.

Along the Hawkesbury River in northwest Sydney, residents have been advised to evacuate from Sackville, Sackville North, Cumberland Reach, Lower Portland, PItt Town, Pitt Town Bottoms, Cornwallis, Richmond, Cattai and Agnes Banks.

The river was rising toward major flood levels at North Richmond on Saturday morning, and is expected to peak in the afternoon, the Bureau of Meteorology said.

The water spilled from the Warragamba dam, southwest of Sydney, flows into the Nepean River in the city's west before merging with the Hawkesbury River in the north.

Residents in some areas of the catchment, along the Nepean at Camden and Menangle and the Hawkesbury at North Richmond, were warned to prepare to evacuate as rivers started to rise on Friday.

Those who remain may find themselves trapped without power, water and other essential services and it could be too dangerous to rescue them, the SES warned.

June is the third consecutive month the dam has spilled.

Premier Chris Minns said on Friday flood-prone communities knew what they needed to do when rivers rise.

"They're pretty adept, and used to, making sure they're accessing the latest information and acting on it quickly," he said, adding the state needs to get more used to extreme weather.

The surface trough that delivered the heavy rainfall began moving south on Friday afternoon, with rain continuing in the Illawarra and south coast as the trough moves out to sea.

Victoria's east may have some showers as the trough makes its way south on Saturday but is unlikely to face the brunt of the rain system.