All indications are for SA to be just as hot until the weekend, when a weak cooler change arrives, according to weatherzone.com.au.
If Adelaide also reaches 40 degrees on Thursday and Friday, it will equal the longest such hot spell in 101 years.
In January 2006 there were also four consecutive days of 40 or hotter.
In Victoria, emergency services remained on high alert as temperatures climbed into the 40s, too.
Melbourne reached a peak of 43.4deg – the hottest day in three years.
Victorian temperatures are forecast to reach similar maximums over the next four days.
It’s that run of extreme temperatures which has weather forecasters talking about the heatwave being among the worst in 100 years in Victoria, too.
Laverton’s temperature was sitting on 41 at midday and still climbing, with many Victorian temperatures recorded in the mid 40s farther north across the state.
“Nhill, for instance, hit 41 degrees by midday,” weatherzone.com.au meteorologist Matt Pearce said.
“Northerly winds carried extremely hot air down from the interior of the continent towards Victoria.
“These northerlies are the result of a persistent and slow-moving high pressure system out in the Tasman Sea.
“This high looks like remaining in place for the next week.
“So we are expecting this extremely hot weather to persist right through into the weekend.”
In addition to the high temperatures, the dry northerly winds are also sending fire dangers to extreme levels in many districts.
As a result, a total fire ban is in force for the North Eastern, Central, North Western and South Western Total Fire Ban Districts.
“The bad news is that there is no rain in sight for the parched state,” Pearce said.
“Coming hot on the heels of one of the driest springs in years, the lack of rainfall through January and now heading into February is a cause for some concern.”