Temperatures across South Australia are running 10 to 12 degrees above average and some regional centres could post record highs as the state swelters through heatwave conditions.
The severe weather has prompted warnings from emergency and health authorities for people to take care, as the state's hospital networks start to track heat-related admissions.
Authorities are particularly concerned about the impact on those most vulnerable, including the homeless, the elderly and those with medical conditions.
"Heat is the worst of our natural emergencies with excess hospital presentations, ambulance transfers and even people potentially dying," Chief Medical Officer Paddy Phillips said.
"We want to prevent that."
Among the hottest spots across South Australia on Tuesday were Tarcoola where the mercury hit 49C and Port Augusta where it reached a record 48.9C.
A number of other centres posted highs in the mid-40s.
In Adelaide, the temperature climbed towards 42C by mid-afternoon after a maximum above 40C on Monday.
Similar temperatures across SA were forecast for Wednesday before slightly milder conditions pushed through the state on Thursday.
Bureau of Meteorology regional director for South Australia John Nairn said the heatwave had its origins in the severe weather that baked Queensland late last year.
"Since then we have not had a weather event that has pushed the hot air out of the continent and it's been recirculating back and forth," he said.
"It's basically a very large pool of air that's been building and that's not being shed."
SA's State Emergency Service has issued an Extreme Heatwave Emergency Warning and the state government has declared a Code Red for Tuesday and Wednesday.
The Code Red triggers extra funding so services for the homeless can be extended while a special phone line will also operate for the next two days, providing regular checks on the elderly and others at risk from the extreme conditions.
The severe conditions also took their toll on cyclists in the Tour Down Under with both the first and second stages shortened because of the heat.
It was also tough for the Indian and Australian cricketers who faced off in a one-day international at Adelaide Oval on Tuesday, though no changes were made to playing conditions.
Amid the heatwave, the Australia Institute released a report that suggests Adelaide could experience nearly three times as many days over 35C by 2090 unless action is taken to better tackle climate change.
"Adelaide already has some of the hottest weather of any Australian capital city and, unless we do more to tackle dangerous global warming, that is only going to get worse," the institute's projects manager Noah Schultz-Byard said.