South Australians are being warned of high temperatures, winds, dust and significant fire danger, with a high of 36C forecast for Adelaide on Thursday.
CFS state duty commander Yvette Dowling said total fire bans were expected throughout most of the state.
"For those areas of the state with total fire bans, we are asking the community to cease any risky activities, such as angle grinding," she said on Wednesday.
"Farmers currently harvesting their crops should today remind themselves of the Harvesting Code of Practice.
"They should be monitoring local weather tomorrow and stop harvesting when conditions worsen."
Across the state, highs of 41C are expected at Coober Pedy and Port August, while Whyalla and Port Pirie should reach 39C, and significant dust is expected to worsen conditions in some areas.
But Bureau of Meteorology forecaster Mika Peace said relief was in sight, with a cool change due to sweep through late Thursday.
She said temperatures will drop by about 20 degrees on Friday.
"We are forecasting hot and windy conditions before the change, and strong winds following it so if a fire has started, it will move quickly," she said.
Australian Associated Press