The company that manages South Australia's power poles and wires says blown fuses, not a lack of electricity supply, are to blame for blackouts that hit Adelaide on its hottest ever day.

About 25,000 customers lost power last night as transformers in several areas crashed, after Adelaide recorded a top temperature of 46.6 degrees Celsius.

SA Power Networks (SAPN) spokesman Paul Roberts said 3,000 megawatts of power was still being used at 10:00pm as residents tried to cope with the temperature still hovering around 35C.

He said the system's safety switch set-up prevented more widespread and longer-lasting blackouts.

"The fuses on the transformer did their job and they failed first to prevent a catastrophic failure of transformers, which meant that's why we could get everybody back overnight," Mr Roberts said.

"If we had those fuses operating, those transformers would have been much more severely damaged and would've all needed to be replaced."

Only about 500 homes and businesses were still without power at 7:00am (ACDT).

Mr Roberts said it was "a great effort by our crews".

"We understand customers would be inconvenienced by these outages, [but] given the number of outages affecting small localised groups of 50 to 170 customers, the crews did a great job to restore most people's power before first light," he said.

The largest blackout was at Fulham Gardens, where 15,000 customers were without electricity.

SA Power Networks said it was caused by a substation fault.

The SA Government says AEMO ordered the generators turned on to deal with a supply shortfall in Victoria. ( Supplied: SA Government )

Debate over privatising generators

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

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

The Liberal Government plans to privatise the generators.



Labor has called on them to rethink their decision.

Opposition energy spokesman Tom Koutsantonis said it was lucky the generators were there, saying without them there could have been load shedding.

"I think the Premier needs to rethink his energy policy and abandon his plans to privatise these generators for the private sector because once we sell them, like ETSA, it's gone forever," he said.

"And next time there's a heatwave like this, we'll be without power."

Energy Minister Dan van Holst Pellekaan said they would always be a back-up.

"We will lease them with very strict conditions that means that they will always be available in times of very, very tight supply," he said.

Petrol station goes up in flames

Cars and petrol bowsers at an OTR service station at Dry Creek caught fire, causing about $150,000 worth of damage.

Loading

Emergency services attended the blaze on Vater Street, just off the Salisbury Highway at Dry Creek just after 7:30pm.

The fire was spreading to the canopy above, but a worker managed to isolate it.

Fire crews were still investigating the cause, but said it might have been related to LPG.

All occupants evacuated the petrol station safely.

The petrol station is closed.

"Once we are confident the site is safe for our guests and team, we will announce that the site is open again for trade," an OTR spokeswoman said.

"We thank everyone for their concern and appreciate the emergency service personnel and firefighters who have assisted this evening."