The heatwave that baked large parts of south-eastern Australia last week is being blamed for a large spike in the number of deaths in Victoria.

More than 203 deaths were reported to the coroner, more than twice the average.

The Victorian Institute of Forensic Medicine expects the number of deaths to reach that of the unprecedented heatwave in 2009, which is thought to have killed more than 370 people in Victoria alone.

Temperatures across the south-eastern states regularly pushed above 40C for several days as the heatwave gripped the region.

The institute's director Stephen Cordner says the heat affected the most vulnerable people in the community.

"The largest number would have been those people elderly pre-existing problems such as artery disease, lung problems, and also those with psychiatric problems," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 2 minutes 47 seconds 2 m 47 s Coroner's figures show heatwave a major disaster ( Simon Lauder ) Download 1.3 MB

"Also those who are isolated without those to look out for them."

Mr Cordner says the loss of life is a disaster.

"That's the ordinary English word for the excess deaths that happen as a result of a heat wave," he said.

Ambulance Victoria says it received a 700 per cent rise in the number of call-outs it received for cardiac arrests on Friday, when temperatures spike at almost 44 degrees Celsius.

At one point paramedics were receiving a call every six minutes reporting cardiac arrests.

Across the state last week paramedics treated more than 500 people for heat exhaustion and received 208 calls about cardiac arrests.

Sixty children were discovered locked in cars during the extreme weather.

In South Australia the ambulance service saw an increase of 400 emergency and urgent incidents, from Monday to Thursday, compared to the same period last year.

"That's an average of 100 more incidents per day and a 17 per cent workload increase," Robert Morton of the SA Ambulance Service said.

"We were well prepared for this heatwave and rostered on additional emergency call takers and on-road clinical staff throughout the heatwave and across the state," he added.

Last week saw Melbourne endure its longest run of 40C days since 1908 and on Thursday Australian Open officials applied the extreme heat policy as the temperature reached 43.4C.

The same day Adelaide was confirmed as the hottest city in the world.

Canberra hit a high of 40.2C on Wednesday, nudging the January record set in 1968 but falling shy by just 1.2C.