Portland police Sergeant Martin Flannery said the report was received on Friday afternoon but by the time police arrived the driver had gone.

"The report suggested the dog had been locked in a car with the windows up for 20 minutes in Percy Street," he said.

"It's warming up and timely to remind drivers that you should never leave children or animals in your car even if you think it's only going to be for a short time

"People need to be very aware that temperature inside vehicle can climb very quickly to life-threatening levels," he said.

Studies have shown that even when it's 22 degrees outside, the temperature inside a vehicle can climb to almost 50 degrees in an hour.

If it's hotter outside the internal temperature in a vehicle can rise to unbearable or life-threatening temperatures, more than 75 degrees Celsius.

A parked car can become 30 degrees hotter than the outside temperature with 75 per cent of the heating occurs in the first five minutes and 90 per cent in the first 15 minutes.

Leaving the window open has minimal affect on reducing the internal temperature of the car (only one degree Celsius when one centimetre open).

Children are particularly at risk because they lose fluid quickly and dehydrated children are at risk of suffering potentially life-threatening heatstroke.