A bushfire on Kangaroo Island is "virtually unstoppable" as it rages under extreme conditions with authorities fearing shifting winds will add to the danger zone.
The blaze near the Ravine Des Casoars wilderness protection area jumped containment lines on Friday and was declared an immediate threat to lives and homes in the area.
By mid-afternoon, it had burnt through 14,000 hectares as it spread into the Flinders Chase National Park and continued to resist efforts by about 150 firefighters to bring it under control.
Locals and tourists had been urged to leave the area with a luxury resort also evacuated, apart from a skeleton staff.
However, Country Fire Service chief officer Mark Jones said it was disappointing that some had not heeded warnings and had chosen to stay.
He said for them, it might now be too late and they should seek shelter.
Mr Jones said there were no confirmed reports yet of property losses or any injuries, but he said he would be "astonished" if homes had not been destroyed.
"The resources that are on the ground are having a good impact," Mr Jones said.
"But the conditions and the severity of the fire means that it's virtually unstoppable at the current time.
"The visibility is extremely poor, even for our aerial bombers, it's difficult for them to see the fire line where they wish to make the drop."
Mr Jones said another fire burning at Duncan on Kangaroo Island also breached containment lines but had since been brought back under greater control.
The escalating danger on the island came as SA endured a day of severe to extreme fire conditions with very high temperatures and rising winds across the state.
In the Adelaide Hills, where 25,000 hectares were blackened two weeks ago, a small fire in hay bales at Woodside was quickly contained.
And a fire burning on Eyre Peninsula was threatening to cut power to the area.
Department of Energy engineer Reinhard Struve said thick smoke could cause a transmission line flashover which would prompt the system to trip, cutting electricity supplies.
In such circumstances, Port Lincoln would be restored relatively quickly with backup generators but isolated properties were likely to be without power for some time.
The Bureau of Meteorology said the cool change moving across SA would reach Kangaroo Island by late afternoon and Adelaide by about 9pm.
The city had a top temperature of 41C ahead of the change, but conditions were forecast to be milder over the weekend with tops in the mid-20s.
