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Distressed dogs locked in cars without enough air are being found in increasing numbers in Auckland this summer, says the SPCA.

Two prosecutions have already been launched and the SPCA says it is prepared to prosecute more.

"Leaving dogs locked in cars, even for a short period of time, is totally unacceptable and anyone caught doing this will face prosecution," Auckland SPCA inspectorate manager David Lloyd-Barker said.

"This is an all too common problem and is the direct result of people simply not being aware of the danger to their animals."

He said the temperature inside a car could rise to 60C very quickly and humidity could double in a matter of minutes.

Dog owners should leave their animals at home when travelling rather than be taken and left in a car, Mr Lloyd-Barker said.