By Jack Gramenz in Sydney

A band of rain in NSW which dumped heavy falls and caused a major dam to spill has moved away, but flood risks remain.

Spills have slowed from Warragamba dam and rain has eased but several riverside communities have been warned to evacuate or prepare to be isolated by floodwaters.

Water overflowing from the dam south west of Sydney is making its way through the Hawkesbury-Nepean system, swelling rivers despite the heavy rainfall easing.

“That does not mean that the risk is not there because what we are going to see now is riverine flooding in many areas,” acting SES commissioner Debbie Platz told reporters on Saturday.

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.

“If people are not evacuating, then we’re asking them to please be prepared for many days of isolation,” Ms Platz said.

The SES began door knocking and moving resources into flood-prone areas as rain persisted throughout the week, Emergency Services Minister Jihad Dib said.

“The community has responded to the SES and to their warnings and to their advice, and when they were told to prepare to leave, they did make that preparation, when people were told to evacuate they did do that,” he said.

But it was disappointing the SES had to conduct 13 flood rescues in the 24 hours to 5am on Saturday.

“People make silly decisions to drive through flooded waters … you’re putting yourself at risk, in danger, but you’re also doing that to the volunteers,” Mr Dib said.

More than 2000 volunteers have been involved in the SES operations.

Warragamba dam outflows have slowed but it may take a few days to return to normal, WaterNSW chief executive Andrew George said.

“Inflows are declining though which is good news for the communities downstream,” he said.

Spills from the dam southwest of Sydney flow into the Nepean River in the city’s west before merging with the Hawkesbury River further north.

Roads have been flooded as dams spilled after heavy rain in parts of coastal NSW. (Dean Lewins/AAP PHOTOS)

June is the third consecutive month the dam has spilled.

The Hawkesbury was rising toward major flood levels at North Richmond on Saturday morning, but appeared to peak below that level shortly after 8am.

The river has continued to fall throughout Saturday, but is expected to remain above minor flood levels into Sunday.