"Within 10 minutes the temperature can reach a deadly 40C in this heat - even in the shade and with the windows down. They will cook."
Dogs don't sweat but begin panting when over-heating, unable to cool themselves down, he said.
Animals suffering from heatstroke pant heavily, profusely salivate, have extremely red gums and tongue, lack co-ordination, can begin vomiting and have diarrhoea and soon slip into unconsciousness.
This can result in death.
"They need a lot of water to cool down. Their heart begins to race and they soon lose consciousness quickly. Then they can die. They cook from the inside.
"Even if you get to them, they could still be seriously brain damaged ... leave them at home under shade with lots of water. Don't take them out in the car."
Some people have window fans installed in their cars for pets - but these lulled pet owners into a false sense of security as they didn't work, Mr Warren said.
"All they do is circulate the hot air inside the car."
Mr Warren holds an inspector's warrant which gives him the licence to break into cars to get distressed animals out.
"A dog can only withstand higher temperatures for only a short time before irreversible damage is done."
If you see an animal locked inside a car, especially if is under stress or panting profusely, call the SPCA on (06) 377 1912.