Adelaide is forecast to have the hottest Christmas Day for eight years, with temperatures of 37 degrees forecast.
Parts of the state’s south, meanwhile, are expected to nudge 40 degrees.
Increasing winds on Boxing Day will elevate the fire risk, with gusts of between 50 and 80km/h predicted.
South Australian Premier Peter Malinauskas said the weather on Christmas Day will be a “belter”.
“It’s going to be 37 degrees and hot in the evening,” he said.
“That does, of course, elevate the bushfire risk.”
The Mount Lofty Ranges and west coast of the state will be under total fire bans.
Locals have been warned not to take risks, with the state seeing some of the driest weather for years.
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“For both Christmas Day and Boxing Day at the very time that a lot of people around our state will be relaxing there will be others on high alert desperately hoping their pager doesn’t go off to respond to a fire that has been caused unnecessarily,” Malinauskas said.
Country Fire Authority President Brett Loughlin warned anyone who gets new power tools for Christmas not to go tinkering with them in the garden while the fire danger is high.
“Any fires that start will spread rapidly,” he said.
John Fisher from the Bureau of Meteorology warned of a ”short-lived burst of heat” ahead of a windy Boxing Day.
“That is elevating the fire danger rating throughout the state,” he said.
Malinauskas also urged people to check on their neighbours during the Christmas heat.
Fire may have been deliberately started
Loughlin said he was “sick to the stomach” to hear a fire south of Adelaide yesterday was being probed as suspicious by SA Police.
Malinauskas said the fire on Education Rd in Onkaparinga was “benign” but served as a warning about the “precarious” conditions.
Four volunteers suffered minor injuries while fighting the blaze, including from falling trees, but no properties were lost.
“Even relatively basic fires can have severe consequences,” Malinauskas said.