Warrnambool police Sergeant Tom Morris said emergency services were called to the hospital just before 11am as the temperature started to head towards a predicted top of 34 degrees.

"The young girl got the keys off mum, but the wind has blown the vehicle door closed and the child has been inadvertently locked in the car," he said.

"Emergency services were called and the fire brigade officers were able to unlock the vehicle and free the child.

"There was no suggestion she was left deliberately locked in the car."

A fire brigade spokesman said the service had equipment to slightly ease open the door of the Honda CRV which allowed the vehicle to be unlocked and the girl freed.

In Victoria it is an offence for a person responsible for a child to leave the child unattended for any longer than is reasonable, without making appropriate arrangements for the child's supervision and care.

That includes leaving a child unattended in a car.

The penalties for leaving a child unattended in a car in Victoria include a fine of up to about $4000 and/or a maximum of six months' imprisonment.

Sergeant Morris took the opportunity to request parents and guardians be aware that leaving a child in a car was a criminal offence, and those charged could be summoned to appear in court.

"It is an offence. Generally we have one or two a year and a decision to issue a charge depends entirely on the circumstances," he said.

"We will issue a charge when kids have been left in cars outside poker machine venues or licensed premises," he said.

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