A massive storm front moving east across NSW has seen a man killed by a fallen tree, with thousands of others left without power after heavy rain, winds and lightning recorded across the state.

The elderly driver has not yet been formally identified, but it is believed his car was struck by a falling tree at about 3:50pm on Lachlan Valley Way, between Cowra and Gooloogong.

At the time, the Bureau of Meteorology reported Cowra's wind gusts to be around 117kph. Wind gusts of 120kph were recorded at Trangie west of Dubbo and 113kph at Cabramurra.

Traffic was diverted away from the scene, with both civilian drivers, including those with heavy farming vehicles - and emergency services personnel clearing roads of fallen trees and debris.

NSW State Emergency Service crews have responded to more than 2250 calls and responded to more than 1800 incidents in 24 hours, predominantly for fallen trees and property damage.

More than 120,000 residents were left without power and 300 electrical hazards were reported across the state.

Severe thunderstorms then combined with a low-pressure weather system, which lasted until Saturday.

Friday will see the worst of the rain, with up to 100mm predicted in some areas.

Emergency services are still tallying the aftermath of severe storms that pounded New South Wales' Central West and east coast, causing power outages, destroying infrastructure, damaging homes.

In a statement, the SES said "The storms which commenced on Wednesday 15 January were severe and deadly," adding that another search was underway for a man feared missing in floodwater at Limpinwood. The service had more than 2100 volunteers active in the field, with a contributed total of over 50,000 operational hours as part of the statewide response.

More than 155,000 residents experienced blackouts during the peak of power outages.

Newcastle bore the brunt, with more than 60,000 power users affected, with 31,000 outages in Sydney and 4000 on the Central Coast, distributor Ausgrid said.

Almost 90,000 customers were still without power about midday on Thursday, with Ausgrid blaming more than 300,000 overnight lightning strikes for the outages.

Supply to 55,000 customers in the Blue Mountains, Sydney's west, the Illawarra region and the south coast was impacted, with 20,000 since restored, Endeavour Energy said.

The heaviest rainfall came on the south coast, where 127mm fell at Eurobodalla and 102mm at Barlows Bay in the 24 hours to 9am on Thursday.

A natural disaster has been declared for Maitland, Port Stephens and Snowy Valleys, an important threshold for both government support and insurance providers to offer assistance.

Member for the Riverina Michael McCormack said the list of LGA's receiving assistance was "not an exhaustive list," adding that "the State [government] will continue to work closely with councils in the days and weeks to come."

“I have spoken to the Federal Minister for Emergency Management of Australia, Senator Jenny McAllister and the Shadow Minister, Senator Perin Davey, about the widespread damage across the Riverina region.

“I have also received detailed updates this afternoon from WWCC, Coolamon and Cowra General Managers Peter Thompson, Tony Donoghue and Paul Devery respectively as well as Ray Johnston from the Cowra SES.

“Whilst I acknowledge that the State first needs to activate the necessary declarations for the Commonwealth to act, the Senators and State MPs in these Ministerial and Shadow Ministerial roles are now well aware of the extent of the damage, particularly through Wagga Wagga, Gumly Gumly, Downside, Marrar, Cowra and elsewhere locally from Wednesday’s wild weather."

Across the region, structures were ripped from their foundations, cargo from trains and cattle deaths recorded from damaged infrastructure and falling power lines.

“I will continue to work with local councils to see what further assistance may be required as assessments and clean-ups continue.

Thanking emergency services, volunteers and Defence personnel, Mr McCormack said “You always see the best of Australians in the worst of times.”

Total incidents:

Metro Zone: 4616

North Eastern Zone: 177

North Western Zone: 86

Northern Zone: 2574

South Eastern Zone:357

Southern Zone: 342

Western Zone: 374

State HQ: 21

Total: 8547