South Australia's Energy Minister is furious with the Australian Energy Market Operator after tens of thousands of South Australian homes were blacked out last night in scorching conditions.

As the temperature hovered about 40 degrees Celsius at 6:30pm, power was cut to more than 40,000 homes for more than half an hour.

Demand for electricity forced SA Power Networks to implement blackouts, prompting an angry response from the SA Government.

The temperature hit 46 degrees Celsius in outback areas of the state on Wednesday, including Port Augusta and Ceduna, while Adelaide saw a top of 42C.

As many people arrived home from work and cranked up their air conditioners in the evening, SA Power Networks announced it would start load shedding to cope with demand, plunging some areas into blackouts.

Thirty minutes after SA Power Networks announced the outages, it tweeted the load shedding had ended.

"The Australian Energy Market Operator (AEMO) has instructed us to commence 100MW rotational load-shedding via a government-agreed list due to lack of available generation supply in South Australia," the power provider said.

"This issue is due to a lack of generation supply and we are required to operate at AEMO's instruction."

South Australian Treasurer Tom Koutsantonis was angry about the outage, blaming the national market operator.

"We had some people tonight without power because the national market didn't turn on the generation that we had in the state," he said.

"The market operator, who runs the national electricity market, got caught short today.

"There was obviously more demand than they had generation turned on in SA. There was an issue with the ElectraNet transmission lines in Port Lincoln, which meant that the Port Lincoln generators couldn't turn on.

"They were caught short by not instructing the second unit at Pelican Point [in Adelaide] to turn on."

Adelaide's expected top for Thursday is 42C, with Port Augusta, Coober Pedy, Woomera, Marree and Moomba forecast to reach 46 and Tarcoola 47.

Federal Government 'won't politicise' SA blackouts

The reliability of South Australia's electricity supplies has been in the spotlight after a statewide blackout in stormy weather last September, causing the Federal Coalition to criticise the state's renewables-heavy power mix.

Another storm in December forced the power distributor to announce compensation payments totalling $20 million to about 75,000 customers after lengthy blackouts.

Prime Minister Malcolm Turnbull has declared energy security will be the "defining debate" of the parliamentary year, but Federal Energy Minister Josh Frydenberg told the ABC the Federal Government would not try to make political gains on Wednesday's forced blackouts.

"Well we're not politicising the fact that there is an insecure energy system in South Australia and that high renewable energy targets, be it in that state or in other states, put in place by Labor governments is going to bring great instability," Mr Frydenberg said.

Mr Frydenberg said the Australian Energy Market Operator disputed some claims that it was to blame and it was preparing an "urgent report" on the blackout.

"The point in South Australia was that there was a lack of supply because the wind was only down to providing 2.5 per cent of South Australia's energy needs," he said.

"That's a lot less than is otherwise expected and that is one of the problems we have with intermittent sources of power."

Heatwave to intensify before the weekend

Weather forecasters say rising humidity will increase the severity of current heatwave conditions and health officials have urged groups such as the elderly to ensure they use available air conditioning whatever it adds to their power bills.

The weather bureau said South Australians could expect little relief from the heat until late on Saturday or early Sunday and forecasters said a burst of humidity would increase the severity of the heatwave before the weekend.

Forecaster Matt Collopy said the bushfire danger could rise in some areas over coming days.

"We're a little concerned about eastern parts of the state [for Thursday], but the fire weather team are working on that and working with the Country Fire Service on [assessing] the fire conditions," he said.

"But primarily this is a heat event rather than a bushfire event."

SA Health chief medical officer Paddy Phillips said vulnerable South Australians, including elderly people, needed to ensure they turned on their air conditioners, even if the cost of electricity concerned them.

"I think people should think about the false economy of saving a couple of dollars in electricity during this prolonged heatwave," he said.