Electricity demand has jumped as people rush to keep homes and businesses cool, though heatwave states have been assured there's enough supply to ward off widespread outages.
South Australian Premier Peter Malinauskas said demand on the network was "extraordinary" but still off the peaks seen in other times.
"So for as long as that trajectory continues, there's no suggestion of any risk at this stage," he told ABC Radio.
Adelaide sweltered through its hottest night on record on Monday and the heatwave impacting South Australia and other southeastern states is continuing into Tuesday.
Evenings are among the toughest times for energy networks as solar generation starts to wind down just as people return home and switch on their air conditioning units.
During these periods of spiking demand, the market seeks generation and supply from more expensive sources than solar, sending wholesale prices higher.
Tony Wood, energy analyst from the Grattan Institute think tank, said South Australia's overnight spot prices peaking at $20,300 per megawatt hour were "pretty well the maximum".
"That just tells you that things were very, very, very bad indeed in terms of supply and demand," he told ABC Radio.
"What that's basically saying is, we need everything to just be online or in some cases, they even need some industrial customers who can reduce their demand."
Fortunately, all major coal power stations and gas generators have been up and running, keeping at bay any major supply issues, including blackouts.
"I'm not saying that we're going to lose power, but this is as tough as I've ever seen it," Mr Wood said.
Victorians are also experiencing the extreme heat, with Melbourne set to swelter through its hottest day since the devastating Black Saturday bushfires in 2009.
The state's energy minister, Lily D'Ambrosio, said Victoria had "quite healthy" electricity supplies.
"Despite the fact that today we're looking at new records being broken, the market operator is very confident that we have more than sufficient reserves in place to meet our electricity needs today," she told reporters on Tuesday.
Yet with multiple fires burning across the state, the energy minister warned local outages could be caused by damage to electrical hardware and infrastructure.
Mr Wood said surging spot electricity prices would have minimal impact on annual household power costs.
Wholesale prices make up just 30-40 per cent of bills and prices tend to average out over the year to around $100 a megawatt hour, or less.
"These prices won't last forever, they're more of an issue for the market and generating supply to respond to the demand we're seeing, and the weather patterns we're seeing," he said.
Mr Wood said the pressures on the electricity system during extremely hot weather underscored the need to build transmission to better connect different parts of the network, and the need to "aggressively" roll out renewables.
