A bushfire ripped through stubble on Eyre Peninsula but South Australia has emerged largely unscathed after a day of catastrophic conditions.
A watch and act message was in place late on Friday for the fire at Cummins.
The Country Fire Service said the blaze was burning uncontrolled and could threaten people and property in the area.
Another at Lobethal, in the Adelaide Hills, was quickly contained after breaking out on a farming property.
The two incidents came on a day when authorities warned of catastrophic fire conditions in the state's mid-north and extreme conditions across another five districts.
The CFS said the combination of high temperatures, strong winds and lightning could result in some properties in the worst areas being impossible to defend if a fire broke out.
The Bureau of Meteorology said the challenging conditions were the result of a trough moving across the state, bringing strong winds ahead of a cool change.
After sweltering through 43C on Thursday and 36C on Friday, Adelaide was forecast to have a milder top of 30C on Saturday.
However, the heatwave conditions were set to continue across the north of the state with temperatures staying in the mid-40s in some regional centres.
On Friday the mercury soared to 48.1C at Tarcoola, the town's hottest December day on record.
