Rolling blackouts could come without warning across South Australia as the heatwave puts intense demand on the state's electricity network.
Homes and businesses could lose power for 30 minutes at a time, with blackouts to roll across Adelaide's suburbs and country areas according to a pre-determined schedule.
The state government's energy market programs executive director Vince Duffy says it's still hoped that power cuts can be avoided.
"At this stage it looks like the general load shedding is unlikely but it's still a possibility," Mr Duffy said.
"There is a very tight supply balance across the Victorian-South Australian region predominantly associated with the extreme heat conditions.
"As temperatures rise we do have a very significant increase in electricity demand."
Mr Duffy said there had been two failures in generating capacity with a plant in Victoria undergoing repairs and one unit at Adelaide's Torrens Island power station also out of action.
Both were expected to return to service on Thursday.
There is also a chance the Basslink interconnector between Victoria and Tasmania may be shut down as a precautionary measure to maintain services in both states.
If power is cut across SA, individual customers are unlikely to get warning and those with special needs for continued electricity supplies have been advised to plan ahead.
South Australian Premier Jay Weatherill says the Red Cross will also make checks on vulnerable people affected by any power cuts to ensure they are coping.
In Adelaide, the temperature failed to reach the forecast maximum of 45C on Wednesday, making it to 43.7C.
A maximum of 46C is forecast for Thursday, which could threaten the record high in the city.
The city sweltered through 45C on Tuesday, just one degree short of its all-time high of 46.1C set on January 12, 1939.
SA Health said that in the first two days of the Adelaide heatwave, 70 people presented to South Australian hospitals with heat-related conditions.
The SA Ambulance Service had been bracing for Wednesday to be the busiest day of the week, saying the third day of a heatwave typically has crews under the most pressure.