Large plumes of smoke and ash could be seen across the Eyre Peninsula and nearby residents were evacuated from their homes as a precaution, the Australian Broadcasting Corp. reported.
There were no initial reports of any damage or injuries.
The fire broke out at Mungerowie Scrub, west of Port Lincoln, and advanced to just over 4 miles from the city.
Malim Watts of the County Fire Service said the intensity of the fire has been reduced but homes could still be at risk.
"I can't emphasize enough the fact that people need to be vigilant," he said.