Three dead as 'once in a decade' storm worsens

Three people have died as the Hunter region cops the worst of the cyclonic conditions battering NSW.

A fallen tree blocks Pitt Rd after a storm at North Curl Curl on the Northern Beaches of Sydney on April 21, 2015. (AAP Image/NEWZULU/CRAIG WILLOUGHBY)

Three elderly people have died amid floodwaters north of Newcastle.

Two men and one woman were trapped in their Dungog houses when floodwaters surged in the early hours and NSW Police have confirmed their deaths. According to the Bureau of Meteorology, the upper Hunter region of Dungog has had 312mm of rainfall within 24 hours.

The news follows dramatic footage of a house floating down a street in Dungog as the Hunter region cops the worst of the cyclonic conditions battering NSW.

The east coast low is expected to pound NSW for another 12 hours before easing.

The SES says the conditions are the state's worst in five years.

Deputy commissioner Steve Pearce says more than 20 people have been rescued from floodwaters.

More than 4000 calls have been made to SES over the past two days.

A hundred schools have been closed, a cruise ship remains stranded outside Sydney Heads and thousands of trees and hundreds of power lines are down, leaving about 215 thousand properties without electricity.

'We will get to you'

Meanwhile NSW Premier Mike Baird is asking people to be patient as emergency crews deal with life-threatening situations during the storms battering the state.

Mr Baird says people need to be patient while authorities focus very clearly on the critical services in health and aged care.

He said there had been more than 4500 calls for assistance and up to 1000 calls to triple-zero.

"We will get to you," Mr Baird said.

In a life-threatening emergency people should call triple-zero, otherwise the SES number was 132 500.

The premier warned residents, especially in the Hunter and Central Coast regions, not to enter floodwaters.

"Many flood rescues have been from people entering floodwaters they shouldn't be entering, he said.

"There has been over 47 flood rescues. Over 200,000 homes and businesses that have lost their power."

Emergency Services Minister David Elliott described the weather system as a "one-in-a-decade storm".

The 500 SES volunteers were risking "life and limb" to ensure that the people of NSW got through the storm.

"Today's events are going to test our emergency services," MrElliott said.

SES Commissioner Adam Dent said people should hold off on non-essential travel.