Half of Australia is experiencing a heatwave this week due to hot air pushed east from Western Australia.
Sydney residents are being warned that temperatures will soar into the low-or-mid 40s on Saturday.
Senior forecaster with the Bureau of Meteorology Sarah Scully has told the ABC, strong wind conditions will also increase the fire danger.
"Extreme fire dangers across southern South Australia, eastern South Australia, and northwest Victoria, and southeast New South Wales, so it's a fairly broad heatwave and fire danger event over the next couple of days."
The bureau predicts New South Wales will be the focus of the heat over the weekend, as a cold front brings relief for W-A, the Northern Territory, and South Australia.
The bureau has issued heat wave warnings for the New South Wales Hunter region, Central and Southern Tablelands, South Coast and Western Districts.
Ms Scully says the fire warnings are set to extend to the main parts of Sydney.
"For New South Wales, there will be extreme fire dangers about the inland but also about the Greater Sydney Area as well, with fire weather warnings likely to be issued."
Temperatures in Sydney and Melbourne topped thirty degrees on Friday as summer announced its arrival.
Heatwaves kept almost 20 government schools across New South Wales closed due to a bushfire warning.
Construction workers braved the rising temperatures while others flocked to the beach.
Steven Pearce from Life Saving NSW says they will need to be on high alert for the peak of the heatwave on Saturday.
"With temperatures forecast into the high 30s and potentially 40s, we really do need to make sure that we've got the right amount of people, and people really understanding that they need to come to a patrolled location."
In South Australia, the heatwave has already made its presence well known, with temperatures at Coober Pedy and Leigh Creek topping 43 degrees on Friday and the mercury at Woomera Aerodrome climbing to 46.4 Celsius.
Firefighters managed to contain multiple blazes in rural parts of South Australia.
The Country Fire Service's CFS Brett Loughlin says firefighters have been combating blazes throughout Friday.
He says the continuous lightning strikes are making work even more difficult.
"Firefighters have been contending with the dry lightning that was forecast, and in the 24 hours so far, over 30,000 lightning strikes have been recorded across South Australia, which has compounded the risks that our firefighters have been dealing with."
A number of schools and pre-schools were closed due to a fire risk, while 13,000 homes and businesses across the state were left without power.
And while South Australia's fire conditions are expected to ease heavy rain and flood warnings will leave emergency crews on high alert.
