Thunderstorms have felled trees and caused power outages across Sydney as damaging winds and large hailstones battered the central and southern parts of coastal NSW.

The Bureau of Meteorology says thunderstorms are likely to continue during the early hours of Wednesday in central NSW before moving towards the northeast by the afternoon.

Damaging winds of about 90km/h pelted Nowra on Tuesday night and were expected to move into Wollongong due to a trough.

Endeavour Energy said electricity cuts were affecting 24,000 of its customers after power lines were brought down in northwest Sydney and the Hawkesbury region on Tuesday night, with 270 electrical hazards needing repairs.

Ausgrid said its power network had been damaged by the intense lightning storm in Sydney, with 72,000 properties left without electricity.

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NSW SES spokesman Jason Simms told ABC radio that volunteers had been called to 600 jobs in the Sydney metropolitan area since 9pm on Tuesday, with most requests for assistance related to downed trees and branches.

A 37-year-old man died after he was struck by a gas bottle in The Rocks just before midnight in an incident police said appeared to be related to the storm.

The bureau predicted winds would strengthen throughout the day but heavy rainfall was unlikely due to fast-moving thunderstorms.

Cooler weather conditions are expected as a cold front moves through NSW from southeast parts of the country.

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A dry air mass means southern parts of NSW could have temperatures drop below 20C, particularly in the Southern Ranges and South Coast region.

Western NSW regions are not expected to have any significant rainfall over the next few days.

Gale warnings are in place for the Eden Coast and strong wind warnings for the Macquarie Coast, Hunter Coast, Illawarra Coast and Batemans Coast.

Hazardous surf warnings are also in place for the Illawarra Coast, Batemans Coast and Eden Coast, with the NSW Police Marine Area Command advising people to consider staying out of the water.

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AAP