Warragamba Dam in Sydney has begun spilling following days of heavy downpours, as residents on the New South Wales south coast count the cost of flood damage.

Key points: Warragamba Dam spills, minor flooding expected downstream

Warragamba Dam spills, minor flooding expected downstream No buildings likely to be inundated

No buildings likely to be inundated Some Shoalhaven residents return to survey flood damage to homes

The Sydney Catchment Authority said Warragamba Dam had begun spilling through its central gate this morning.

It is the first time in two years the dam has spilled, according to the weather bureau, though the maximum spill is now expected to be much less than previously forecast.

Up to 160 millimetres of rain fell in the Wollondilly River upstream of the Warragamba Dam in the 48 hours to 9:00am on Wednesday.

Gordon McKay from the Bureau of Meteorology said the river was expected to peak tonight.

"Further downstream the peak will get through Penrith around 6:00pm this evening and we're expecting the peak to arrive at North Richmond around midnight, and it'll take another three or so hours to get down to Windsor," he said.

"At Windsor we expect the river levels to peak below minor flood levels."

Residents face costly clean-up

A couple walks through floodwater in Sussex Inlet. ( ABC News: John Gunn )

Many residents on the NSW South Coast are still to return home with flood waters in parts of the region yet to recede.

The Shoalhaven region has enjoyed a reprieve from the more than 400 millimetres of rain that has been falling since Monday, with blue skies welcomed by SES unit controller Gerry Sheen.

"I'm doing backflips, absolutely fantastic," he said.

More than 320 properties have been evacuated since Monday and the emergency services have received more than 900 calls for help.

While around Nowra and Shoalhaven Heads the floodwaters have receded quickly, in Sussex Inlet it is a waiting game.

"There's empty bottles and drums and all sorts of things coming down," resident Christopher Sargent said.

Shoalhaven Mayor Joanna Gash said the council was calculating the damage bill and applying for state and federal funding assistance.

In the Shoalhaven region, about 80 homes have been flooded and the heavy downpours have damaged dozens of local roads.

The Environmental Protection Authority has also been monitoring health concerns after the sewage system failed in parts of the region.

Sussex Inlet resident Bill Crothers said it would cost him at least a few thousand dollars to repair the flood damage.

"Inside there was six to eight inches of water throughout the house," he said.

"We got a lot of the furniture up but the walls probably need replacing."

Water levels in the Shoalhaven have now peaked and the rain has eased, but extensive flooding remains. ( ABC News: John Gunn )

He said he had been through similar flooding before, so the downstairs area was tiled, but that clothes and furniture were ruined.

"I'm not sure about the boat and whether the motor has gone under or not. We'll soon see."

Kerry Winterford was rescued from her caravan at Sussex Inlet on Wednesday and said she would stay at the local evacuation centre until the water receded.

"We've been coming down here for close to 20 years now and we've seen floods before, but nothing like this," she said.

"Depending on what the water does, we can't get back to the van park until the water subsides.

"So, I guess we're going to hope they'll keep putting us up here until we can get back to the car."

Anglicare volunteer Ruth Oliver said it was important the community knew they had a safe place to go in a time of need.

"They are calm and I think they feel cared for," she said.

"That's one that I think is important about having an evacuation centre."