New South Wales is set to swelter with near-record temperatures across the state.
Most regions will experience temperatures above 40 degrees and Sydney is forecast to reach 43 degrees.
The Bureau of Meteorology's Regional Director, Barry Hanstrum, says the conditions are exceptional.
"If the temperature reaches 43 degrees in Sydney, that's only happened or been exceeded twice previously," he said.
Mr Hanstrum says the high temperatures are made even more exceptional by the combination of strong westerly winds all the way to the coast.
"It's very rare indeed to see winds of 60 to 80 kilometres per hour in the late afternoon in New South Wales with temperatures in the mid forties."
A cool change is expected to cross the state, with temperatures in Sydney dropping to just 25 degrees tomorrow.
But Mr Hanstrum says it will not come in time to bring relief from the heat today.
"The change is not expected to reach the Illawarra coast until 9:00pm or 10:00pm and won't come through Sydney until the early hours of Wednesday morning," he said.
"We think the temperature will be still hovering in the low thirties around midnight"
Energy Minister Chris Hartcher says New South Wales is prepared for the spike in energy use that is expected to come with today's extreme heat.
Mr Hartcher says there is sufficient capacity to handle the increased demand and further supplies are available if required.
But he says he still anticipates huge pressure on the electricity network.
"It is expected there will be a large increase in the amount of electricity consumed," he said.
Surf Life Saving New South Wales is boosting its resources to cope with an expected influx of people to the state's beaches today.
The organisation is rostering more staff and is considering extending its patrols.
State Manager Dean Storey says he is anticipating a busy day.
"Lifesaving services across the state are expecting a lot of people to be heading towards the coast," he said.
"So use a bit of common sense, play safe, swim at a patrolled beach between those red and yellow flags, and if you're boating or rock fishing, always wear a lifejacket."
People are also being reminded to look out for the elderly and young children during today's extreme heat.
Major Bruce Harmer from the Salvation Army says sick people will also need attention.
He says the charity's emergency services units are on standby across the state to provide food and water in affected towns.
"We certainly have now mobilised all of our Salvation Army services units in New South Wales," he said.
"They're on standby, we were asked by the Government to put them on standby. Usually we'll be called in, and then we come in and provide whatever support we can, usually in the provision of food."
© ABC 2013
12:38 EST Tropical Cyclone Jack has rapidly developed over the warm waters of the Indian Ocean in the past 24 hours, making it the 10th system to be named this season.