Paramedics responded to 1696 incidents of people being locked in vehicles in the year to August – 73 times more often than in 2016.

Most of the children rescued were younger than 13 years old.

"This figure should be zero," Acting Health Minister Jenny Mikakos said. "But despite all of the heat warnings and significant penalties, children are still being put at risk of serious heat-related injury or death by being left unattended in parked cars."

Ms Mikakos said three children had died over the past four years after being left in cars. 

She said people who left children unattended faced fines of $4000 and six months imprisonment.

In the year to August five people faced court and 21 were issued with summons for leaving children unattended, Ms Mikakos said.

The release of the troubling statistics came as health authorities and emergency services issued a warning that Victoria faced above average temperatures this summer.

They have urged Victorians to take precautions and look out for vulnerable people in the community.

The temperature is expected to reach 35 degrees in Melbourne today and 31 Thursday before cooling off at the end of the week.  

Ambulance Victoria state health commander Paul Holman said the heatwave in 2009 had been the most troubling experience in his 40 years in the ambulance service.

"Nothing has left a greater impression on me than the heatwave in 2009 where 500 people died in three days," he said.

Mr Holman said the death rate went "virtually unnoticed" at the time because many of those who died were elderly, infirm, socially isolated or poor.  

"Heat does kill. It's well known. I never want to live through 2009 again. It was a horrific experience over that period of time."