Temporary diesel power generators owned by the South Australian Government have been switched on for the first time, as the Australian Energy Market Operator (AEMO) deals with record-breaking heat conditions across SA and Victoria.

Key points: Generators have been switched on to deal with pressure on the energy system in SA and Victoria

Generators have been switched on to deal with pressure on the energy system in SA and Victoria AEMO's chief executive says the demand for power has been higher than anticipated

AEMO's chief executive says the demand for power has been higher than anticipated It came as all-time heat records were smashed across South Australia on Thursday

The State Government said AEMO ordered the generators to deal with a supply shortfall in Victoria.

The diesel generators were installed by the former Weatherill government ahead of last summer as an emergency measure to prevent load shedding blackouts.

But the emergency reserves were not called upon last summer, with the market operator instead paying major industrial power customers to reduce their usage.

After the state endured load-shedding blackouts in early 2017, the former government announced it would lease nine aero-derivative turbines from APR Energy to use to secure the state's power supply.

The turbines were temporarily installed at Lonsdale in Adelaide's south and the former Holden factory in the city's north.

The new power generators were installed at two Adelaide sites in 2017. ( Supplied: SA Government )

The deal for the turbines included an option to purchase them outright at the end of an initial two-year lease period, with former premier Jay Weatherill choosing to purchase them early.

Last year, the current Liberal Government made the decision to privatise operation of the two back-up power stations, declaring the turbines would deliver little benefit for a cost of more than $600 million over their 25-year life.

AEMO chief executive Aubrey Zibelman said the demand for power on Thursday had been higher than anticipated, and the operator decided "having resources in case we lost another generator was a prudent thing to do".

"We have been planning for conditions like today [Thursday] by procuring strategic reserves that will bolster our ability to manage unforeseen incidents across the power system," Ms Zibelman said.

"AEMO has now called on these additional reserves to mitigate the risk of supply shortfalls."

Victorian Energy Minister Lily D'Ambrosio said the state was seeing "an extraordinary heat event".

"It is putting extreme pressure and stress on our energy system," she said.

While confident there would be enough supply to get through the night, Ms D'Ambrosio called for residents to be scarce with their power usage.

"What we would ask Victorians to do is just be aware and be mindful that the activities that we undertake [on Thursday night] when we're at home does put that further pressure on our energy system," Ms D'Ambrosio said.

"We are confident that we'll have sufficient supply for that critical period."

Ms D'Ambrosio encouraged Victorians to delay using their washing machines and dishwashers if possible, and for healthy people to consider turning their air conditioners to 24C to save energy.

"These are small things but they can add up to actually help us manage the situation," she said.

Heat records tumbled across South Australia on Thursday as Adelaide hit a sweltering 46.6C, topping its 1939 heat record of 46.1C.

It also topped the nation's previous capital city record of 46.4C set in Melbourne in 2009.

Port Augusta reached the highest temperature across South Australia, peaking at 49.5C just after 4:00pm, while Ceduna set a record for the second day in a row reaching 48.6C.