As the rains ease, winds dissipate and floods recede, emergency services have shifted to clean-up mode, with the damage bill from NSW's once-in-a-decade storm expected to exceed $129 million.

Premier Mike Baird will tour some of the state's worst-affected areas on Thursday, including the devastated Hunter region where cyclonic winds, heavy rain and flash flooding claimed six lives, submerged streets, swept away houses and caused extensive damage to buildings and transport infrastructure.

The NSW State Emergency Service said it had received 18,000 calls and 12,611 requests for assistance, and performed 139 rescue operations since 10am on Monday.

Volunteer crews from Victoria and the ACT have arrived in NSW to assist with the clean-up.

On Thursday, about 200,000 homes across NSW remained without power, while the state's electricity network, Ausgrid, has received 164,000 calls since Monday.

"The biggest areas to clean up will be in the Newcastle area, around Dungog and Maitland," a spokesperson for NSW SES said.

After receiving more than 400mm of rain, Maitland and Dungog were ravaged by flash flooding, which left a trail of destruction as floods subsided.

On Monday, at least four houses were swept from their foundations in Dungog as water roared through the town's main streets.

In total, eight people were killed across the state in connection with the storm.

Robyn McDonald, 70, Colin Webb, 79, and Brian Wilson, 72, died after their assisted care residences in Dungog were submerged by floods.

On Wednesday, the body of an 86-year-old woman was recovered after the car she was travelling in was swept from a road in Maitland.

On Wednesday afternoon, two drivers died and a two passengers were seriously injured when two cars collided in wet conditions on the New England Highway between Singleton and Muswellbrook.

A man died on Wednesday after his ute and a garbage truck collided at Galston, and an 87-year-old pedestrian died after being hit by a car in East Gosford.

On Thursday morning, an evacuation order remained in place at Milperra, in Sydney's south-west, after hundreds of residents were urged to leave their homes as the Georges River burst its banks on Wednesday.

The SES is expected to give the area the all-clear later in the day.

While some showers are expected to hamper clean-up efforts in the Hunter and Sydney regions, senior Weatherzone meteorologist Rob Sharpe said weather conditions would continue to improve throughout Thursday and into Friday.

"Generally, light winds are expected across Sydney and the Hunter region and just a few showers around," he said.

"But people will be seeing the sun and things will be drying out quite a bit today."

In Sydney, the organisers of Camp Gallipoli have postponed the event, during which hundreds were expected to camp in Centennial Park on Friday night to commemorate the 100-year anniversary of Anzac Day on Saturday.

The Camp Gallipoli Foundation said it would advise of the new event details in the coming days.

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