Authorities fear several elderly people may have died due to the heatwave baking southern Australia, after 18 "sudden deaths" in one city on Friday.
"How many of them are associated with the heat is speculative, but it's obviously a high number," South Australia state Health Minister John Hill said.
Of the 18 people who died in Adelaide since midnight on Thursday, 14 of them were elderly.
Sudden deaths are those caused by medical conditions such as heart attacks and strokes, said an ambulance official who confirmed the number of deaths. He said post mortems would determine whether the deaths were heat-related.
Extreme temperatures above 40 degrees Celsius (104 Fahrenheit) have baked Victoria and South Australia states for the past three days, disrupting power and transport and leaving medical services struggling.
Weather officials say if the high temperatures continue until Sunday it will equal the worst heatwave in 100 years.
Melbourne recorded its hottest ever three-day heatwave on Friday, after the temperature hit 43.8 degrees Celsius, the third day above 43 Celsius.
About 90 trains were cancelled in the city due to the heat, as crews repaired buckled rail lines, leaving thousands of commuters stranded.
With thousands of people flocking to the beach to escape the high temperatures, which are continuing in the night, lifesavers in Victoria state launched night beach patrols on Friday.
The high temperatures have led to soaring demand for power to keep air conditioners going, and caused breakdowns in transformers, resulting in outages in Victoria and South Australia, and power shedding to ease demand.
More than 40,000 homes were without power in Victoria on Friday, where there are rolling one-hour blackouts to try and ease the demand on the electricity grid. In South Australia, power was cut to 95,000 homes in load shedding.
Firefighters in Victoria are battling two bushfires which have burnt 2,000 hectares of forest, grassland and private pine plantation.
Fruit growers in South Australia and Victoria said they were battling to save crops in the heatwave. But so far the heatwave has remained in southern Australia and not moved north towards the country's main wheat and sugar crops.