The Bureau of Meteorology has forecast a high of 41C for Adelaide on Friday after the mercury hit almost 42C on Thursday and 39C on Wednesday.
It is tipped to get even hotter in regional South Australia with 44C at Roxby Downs, 43C at Whyalla and 45C at Renmark predicted.
The conditions prompted the Australian Energy Market Operator (AEMO) to issue a lack of reserve notice for Friday afternoon, but SA Energy Minister Tom Koutsantonis said it's unlikely the state's backup generators will be needed.
"There are many stages of lack of reserve notices," he told reporters.
"If we get to the point where we need to step in, we have a state-owned generator that can step in quickly and respond within minutes and we have a battery that can step in within seconds."
The forecast has forced the cancellation of the Bupa Challenge cycling event, involving thousands of recreational cyclists riding the same course as the Tour Down Under professionals.
However, police said many had chosen not to heed warnings and were riding it without support.
"Given the extreme heat, I would urge all riders to make sensible choices today don't put yourself or others at risk," Assistant Commissioner Scott Duval said.
Some relief should reach the city by Saturday with the maximum temperature forecasted to be a more tolerable 35C.
