Drier-than-expected conditions have put Sydney and much of the NSW coast in severe fire danger with the heat unlikely to ease until the weekend.
A large mass of hot air moving across the state on Friday is driving temperatures towards 40C in some parts of NSW with Sydney reaching 36C.
Bureau of Meteorology severe weather manager Simon Louis says there's little difference in temperatures between western Sydney and the city's beaches with the usual sea breeze blocked by strong westerly winds.
"We're expecting the warm conditions to continue overnight particularly for Sydney," he told reporters in Sydney.
Conditions are expected to ease early on Saturday as a cold front moves up from the south of the state bringing light showers and possible thunderstorms.
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"It's not a particularly strong cold change so we will still have fairly warm conditions into the weekend," Mr Louis said.
Friday's high temperatures have caused trains to be replaced with buses from Blacktown to Mulgrave due to the heat affecting infrastructure.
The hot weather also saw the NSW Rural Fire Service raise the fire danger to severe for the Southern Ranges, Illawarra, Greater Sydney and Hunter regions.
Total fire bans are in place across those regions.
Wind gusts are expected to reach up to 80km/h in some areas including Goulburn adding to the risk of dangerous bushfires.
"It's important on the first real hot and windy day (of the season) people take five minutes to discuss with their family what to do in case of a fire," RFS Inspector Ben Shepherd told AAP.
Firefighters are already battling an out-of-control blaze southwest of Canberra.
The 226-hectare bushfire, which started on Thursday night, is burning erratically at Pierces Creek about eight kilometres from the nearest suburb.
Multiple small grassfires are also being reported across the state.
A number of areas set early season records on Thursday with Goulburn (32.2C), Wagga Wagga (37.6C), Albury (37.2C) and Young (34.8C) among those setting new maximum temperature records for this time of year.
