Leaving Vic kids in hot cars 'is torture'

Leaving a child inside a hot car for as little as five minutes is akin to "torture", authorities say.

As temperatures are predicted to soar above 40C on Wednesday, the Victorian Government is taking steps to warn parents about the consequences of leaving children locked inside hot cars in scorching weather.

Speaking at the launch of the No Excuses, No Exceptions campaign on Tuesday, Acting Premier James Merlino said previous messages don't seem to be getting through to parents.

"Just last month, in December, 225 kids needed to be rescued," he told reporters.

"Thirteen children, on a 37 degree day."

Ambulance Victoria's director of emergency services Paul Holman says children left inside hot cars couldn't regulate their temperature, sweat or cool down.

"I think torture is probably the word that comes to mind," he said when asked how children felt.

"Immediately they get dehydrated, and start to go into organ failure in very quick time in those temperatures."

Children's temperatures can rise up to five times faster than an adult's on hot days.

Parents or carers who leave children unattended in a car face fines of nearly $3700 or jail.