A total fire ban is in place across South Australia, with 43C forecast for Adelaide.
Emergency services are warning people to refrain from any outdoor activities which could start a fire.
The forecast for Adelaide on Thursday is 43C, which would be the hottest day since 17 January, when the temperature reached 43.1C.
AAP reports total fire bans are in place for all 15 fire districts in the state, including the Adelaide metropolitan area.
The Country Fire Service on Wednesday contained a bushfire which came close to houses in the Adelaide Hills and destroyed about 1000 hectares of grassland.
Crews remain at the scene, near Rockleigh.
The Bureau of Meteorology said a cool change was not expected across the state until late on Friday.