Victorian paramedics attended more than 600 cases of people locked in cars in the five months to January, with two-thirds of the call-outs for children aged under 13. Most of those cases involved toddlers and newborns.

Released on Tuesday, the Ambulance Victoria data shows of the 620 cases attended by paramedics, 99 people needed treatment and 24 were taken to hospital.

January was the busiest period for paramedics attending to people locked in cars, accounting for a third of all cases recorded during the five-month period.

The data reveals the most common location for children to be reported locked in a car was in a car park or beside a public road.

By postcode, Pakenham had the highest number with 16 reported incidents over the five months, followed by Melbourne and Frankston with 13 each and Narre Warren with 11.

Tuesday's forecast temperature of 32 degrees in Melbourne and temperatures reaching the low to mid-30s in northern parts of the state prompted the government to warn parents and carers to be vigilant. "A car's temperature starts to rise from the moment the door is closed and can be double the outside temperature in minutes," Children and Early Childhood Development Minister Wendy Lovell warned.

The warmer weather is forecast to return during the weekend, with Melbourne temperatures reaching the high 20s before hitting 30 degrees next Monday.

The warnings follow research conducted by the state government, which shows one in three parents admitted to leaving children alone in a parked car.

Ambulance Victoria group manager Brett Drummond said research found that even on a 29-degree day, the inside of a car could reach 44 degrees within 10 minutes. And within 20 minutes the temperature could hit 60 degrees.

"It doesn't have to be a scorching hot day for the car to quickly heat up," he said.

A Victoria Police spokeswoman said the penalty for leaving a child unattended was a $2165 fine or three months in prison.

There is no specific charge related to leaving a child unattended in a car.

The spokeswoman said it was up to the discretion of an officer when laying charges, with adults paying for petrol not necessarily committing an offence.