An emergency warning was in place late on Friday for the fire which broke containment lines earlier in the day amid extreme conditions including high temperatures and strong winds.

The Country Fire Service said the blaze, which had already destroyed more than 14,000 hectares in and around the Flinders Chase National Park, was heading towards Vivonne Bay, on the island's south coast.

A watch and act warning also covered the central town of Parndana, home to about 150 people.

Local residents and others in the area were urged to leave and head to either the towns of Kingscote or Peneshaw, on the east coast.

"There is a real risk posed by this fire. This fire is burning out of control, having breached the control lines," the CFS said.

"This is a dynamic fireground and conditions are continually changing. The fire remains uncontrolled and unpredictable in nature and difficult for fire crews to control."

CFS chief officer Mark Jones there were no confirmed reports of property losses or any injuries, but he said he would be "astonished" if homes had not been destroyed.

He also described the fire as "virtually unstoppable" under the prevailing conditions.

About 150 firefighters worked on the blaze during the day with that number to be bolstered by crews from the mainland across the weekend.

A watch and act warning was also in place on Friday night for a fire burning uncontrolled near Kersbrook in the Adelaide Hills.

The fire was near, but not within the perimeter, of another fire which burnt through 25,000 hectares in the Hills two weeks ago.

The CFS said it had 140 firefighters and 25 trucks on the scene with fire expected to burn for some time.

The escalating danger came as SA endured a day of severe to extreme fire conditions across the state.

Adelaide had a top temperature of 41C ahead of a cool change, but conditions were forecast to be milder over the weekend with tops in the mid-20s.

Australian Associated Press