Storm declared 'natural disaster' as cyclone builds

Thousands of households will endure a fourth night without power and communities are on the brink of isolation as a week of wild weather is declared a natural disaster.

Wind gusts of up to 100km/h throughout the week have left more than 100,000 Sydney households and businesses without power, including tens of thousands severed from the network on Friday night.

Almost 35,000 premises across Sydney, Newcastle and the Hunter were without electricity on Saturday evening, including 7500 in darkness since Wednesday.

The storms, declared a natural disaster in the most severely affected areas, came as a cyclone brewing off West Australia's north coast closed a major port.

The NSW storms triggered 2825 calls for help on Friday night, including four flood rescues, the state SES said.

Warnings are in place for communities and campers northwest of Newcastle, downstream of the Chichester Dam.

"We do currently have some communities and some locations that are becoming isolated, and the warnings reflect that, and we're very closely engaged with the local communities," SES commissioner Michael Wassing told reporters on Saturday.

"Most of our other calls are associated with significant storming impact around the Sydney area, particularly North Sydney."

Meanwhile, strong winds lifted sand off Bondi Beach, blanketing the promenade and car park.

On Friday afternoon at least two people were injured when a large fig tree in Hyde Park crashed to the ground across a footpath and onto a busy street.

Two people suffering minor injuries were transported to the nearby St Vincent's Hospital for treatment, a NSW Ambulance spokesperson said.

Earlier in the week a man in his 80s was killed when a tree fell on his car overnight in the state's central west.

Federal Emergency Management Minister Jenny McAllister declared the wild weather a natural disaster, opening up disaster payments for affected families and businesses.

The declaration applies to the Maitland, Port Stephens and Snowy Valleys local government areas.

"The assistance activated today will ensure communities can access essential supplies and accommodation and ensure councils can start clean up and repairs," Ms McAllister said.

"This is a time when individuals need to think about their own risks and listen to advice."

Heavy rainfall continued through Saturday morning but severe weather subsided into the afternoon.

In Western Australia, gale-force winds were expected along the Pilbara coast as a potential category-three cyclone brews overnight.

The developing low is expected to move west, parallel to the Pilbara coast on Sunday and move southwest and away from the WA coast on Monday.

While the expected cyclone will move offshore before it develops, large waves could cause minor flooding between De Grey and Exmouth.

The Port of Port Headland closed on Saturday in anticipation while all berths were due to be cleared from the ports of Dampier, Ashburton, Varanus Island and Cape Preston by early Sunday morning.

The Pilbara Ports facilitate 43 per cent of the world's iron ore trade.