More than 17,000 people across Sydney were left without power for hours on Wednesday after the hottest day of the year saw temperatures hit 42 degrees in the west and 38 degrees in the city.
Power was restored to most residents and businesses by 8pm after outages in the north, south and west of Sydney started plaguing the electricity network about 3.25pm.
Ausgrid spokeswoman Zoe Allebone said the hot weather tended to put greater demand on the network, with usage "noticeably higher" on Wednesday than the same time last week.
Temperatures peaked at 1pm on Wednesday and by 5pm it was still 31.3 degrees in the city and 41.2 degrees in Penrith.
"Demand for power tends to increase on hotter and colder days as residences and businesses turn on their airconditioners," Ms Allebone said.
She said the outages did not appear to be heat-related.
Wednesday was the fifth day of this summer that temperatures have exceeded 35 degrees, the most since 1990-91.
Thursday will bring some short-lived relief, with a maximum in the city of 27 degrees and 30 in the west, the Bureau of Meteorology said.
Last night, about 2500 people were still waiting for power around Dee Why and North Ryde.
Earlier in the day, 7100 people in the Sutherland Shire were left without power when party balloons ran into powerlines. An outage around Bankstown left 3900 customers in the dark for five hours. Two outages on the north shore also affected 3100 customers for about two hours before power was restored at 6pm.
Grass fires have also broken out near Penrith and near the Hunter Expressway at Loxford, the Rural Fire Service reported.
Some of the world's leading tennis players were left to sizzle at Sydney Olympic Park as play continued in heat exceeding 41 degrees at the Sydney International.
Danish star Caroline Wozniacki was among those frying on court. Luxembourg's Gilles Muller, whose victory over Australian Matthew Barton came just as temperatures hit 40 degrees after 2pm, described the conditions as the toughest he's played in.
One player was also unable to use his phone following the match after it baked in his bag for almost three hours.
Friday may come close to Wednesday's top, at least in the west, with several sites expecting 40 degrees. For now, the forecast is that the city will benefit from a sea breeze, keeping the maximum to 31 degrees.
Out in the state's far west, the mercury may top the 46 degrees recorded in Bourke on Wednesday, with similar scorching highs expected in the town on Friday. Wilcannia may reach 47 degrees, the bureau said.
"While it's definitely hot, so far I haven't seen any maximum temperature records broken for NSW," Acacia Peppler, a climatologist at the bureau, said. "There have been some big heatwaves in recent years, for example in in 2013 and 2014", that will take some beating.
Along with the mercury, water use is likely to have surged in Sydney on Wednesday, in line with a spike in mid-December when a similar burst of heat singed the city.
On December 13, water use reached a 10-year high of 2.171 billion litres in the region covering Sydney, the Blue Mountains and Illawarra, Sydney Water said.
Total water consumption over 2016 totalled 545 billion litres, or an average of 1.49 billion litres a day, the agency said.
On an average day, water use is just under 300 litres a person – the lowest since the 1940s. That compares with a peak year of 1980-81 when average daily water use reached 527 litres on a per capita basis.
Sydneysiders are using much less water overall - even as the population swells to 4.8 million for the region - because of the introduction of dual flush toilets, more water-efficient homes and appliances, and the greater use of alternatives such as recycled water or rainwater tanks, Sydney Water said.
With Michael Chammas
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