The mop-up resumed at first light after severe thunderstorms battered the state overnight.
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Power was cut to about 11,000 homes and businesses in western Sydney and the Illawarra on Tuesday evening, and emergency crews from Endeavour Energy worked to restore power to all but 2,100 customers just before 11pm.
Several hundred customers across the storm-affected area would not have their power restored until Wednesday morning, Endeavour Energy said.
The Bureau of Meteorology had issued a severe thunderstorm warning just after 6pm on Tuesday for large hailstones, damaging winds, heavy rainfall and possible flash flooding.
Endeavour Energy said the power network suffered "extensive" damage in the bad weather, with strong winds bringing down trees onto power lines and lightning strikes damaging two substations.
The NSW State Emergency Service received 385 requests for assistance across the state, a spokeswoman said, including136 in the Sydney area alone.
The damage caused by the severe thunderstorms and winds was mostly related to trees and branches down, and there were no major isolated incidents, the spokeswoman said.
"We had teams until late last night, and they will be resuming at first light," she said.
The SES spokeswoman said the worst hit areas outside Sydney were Bathurst, Cootamundra and Cowra.
Thunderstorms could remain a possibility in coming days, particularly in western parts of Sydney, said Weatherzone meteorologist Kim Westcott.
Time lapse of #SydneyStorm from yesterday evening. Shelf cloud is formed when air rises ahead of thunderstorm gust front, which also generated 91km/h gust at Sydney Airport. No storms for Sydney today! pic.twitter.com/r47sPEDEsz??? Bureau of Meteorology, New South Wales (@BOM_NSW) January 9, 2018
Sydney, though, can expect some relief from the recent heat, with daytime temperatures easing back to more typical levels for January of about 25-26 degrees.
The next bout of heat should arrive from Friday, with the mercury nudging back towards 30 degrees.
The western suburbs will again be in for some hot days, with 35 degrees tipped for Penrith on Friday and another day of 40 degrees for Saturday.
Sunday may feel even cool, with a top of 23 degrees forecast for the city and 28 in the west.
Storms may bring the best chance for more than the odd few millimetres of rain over the next week. Penrith could receive as much as 20 millimetres of rain on Saturday, the bureau said.
Weatherzone is owned by Fairfax Media, publisher of this website.
With Georgina Mitchell