Millions of Australian city-dwellers will get a taste of a spring heatwave that has broken temperature records in three states.

Sydney is forecast to swelter through an expected top of 38C on Wednesday, with Newcastle (39C) and Wollongong (36C) also in the firing line.

Senior meteorologist Angus Hines said the hot conditions stemmed from a “bubble of heat” stretching across central Australia.

Queensland, NSW and South Australia posted their hottest October days on record on Tuesday, with the mercury hitting 46.1C in Birdsville, 44.8C in Bourke and 45C at Moomba Airport.

The all-time temperatures were delivering heatwave conditions and elevated fire danger, Mr Hines said.

Total fire bans have been declared for the regions of Greater Sydney, Greater Hunter, Illawarra/Shoalhaven, Upper C

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