Cars overheat rapidly on a hot day even with the windows down and parked in shade.

Dog owners could be fined $300 if they leave their dogs in their car this summer.

New regulations from October 1 give the police and SPCA officers the right to hand out infringement notices and fines of $300 to people who leave a dog in a hot car.

Bystanders worried about dogs trapped in hot cars should call the police or SPCA to get action taken.

LUKE KIRKEBY Dogs can do little more than pant to cool themselves down.

While calls are often made to local authority animal control officers, only the SPCA and police and Ministry of Primary Industries work under the Animal Welfare Act.

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The SPCA says many dog owners don't realise how quickly cars heat up inside and having windows down or being in the shade makes little difference.

On a 30 degree Celsius day the temperature inside the car can reach 39deg in less than 5 minutes and in 30 minutes it can reach 49deg.

Dogs rely on panting to cool down and in a hot car that's not enough. They can withstand a body temperature of 41deg for only short time before suffering brain damage then death.

When they are suffering from heatstroke, dogs start to pant and drool excessively and lose coordination. As it gets worse, the dog will vomit or collapse.

Manawatu District Council animal control officer Lesley Butler says the council has had five calls for dogs in cars in the last month.

All were about dogs spotted in cars at the supermarket and at The Warehouse.

"I've gone down if nothing else to support the person who made the call while they wait for the SPCA."

She says a dog who is suffering from heat in a car will crawl to the lowest point such as on the floor.

"They will be panting a lot and when it gets really bad they will collapse from heat stroke," Butler says.

"You know, people think 'oh I leave a bowl of water for the dog' but it doesn't really make any difference.

"My advice is leave your dog at home. You think you are taking it out on a little trip. You pop into a shop on the way home, it's easily done. You bump into someone and get chatting and when you come out your dog is dead.

"Just leave it at home. It's not worth losing your pet."