Victorian paramedics say they were shocked to receive 11 reports of children locked in cars during yesterday's extreme heat.

Temperatures peaked around 43 degrees Celsius in Melbourne yesterday, and similar temperatures are expected until Friday.

Ambulance Victoria spokesman Paul Holman says people are risking the lives of their children by leaving them in a hot car.

"You lock your children in a car in this type of weather you may as well put a gun to their head," he said.

"It's absolutely the most dangerous thing you can do."

Paramedics also received 85 reports of heat-related illnesses and dealt with 18 cardiac arrests.

Mr Holman says people need to adjust their lifestyle to the heat.

"You've got to respect this weather, this is not normal, this is extreme weather," he said.

"It is dangerous and you need to look after your family and friends."

Sydney mother may face charges

NSW Police say it is likely a Sydney mother will be charged after leaving her nine-month-old baby in a car.

Officers had to break into the car to remove the crying baby boy when they were called to Lakemba last night.

The 31-year-old mother turned up shortly afterwards and told police she had left the baby in the car to sleep while she was working in a nearby unit.

The baby was not injured.

It is illegal to leave a child locked in a car and parents can face fines up to $22,000.