A dog was found alone in a sealed car, with no water and in direct sunlight, in Castle Hill on Monday.
About 2.30pm, police were called to a Castle Towers car park when someone noticed the dog inside the car, barking in some distress.
Police said an NRMA mechanic had also been called, but he feared for his safety if he opened the car and faced the dog alone.
Officers distracted the animal while the car was opened and managed to restrain it.
They said the recorded temperature inside the car was 37 degrees.
Police tried to contact the owner through his mobile phone and paged him on the shopping centre’s intercom, but got no response.
However, while they waited for Hills Council staff to come and take the dog, the owner suddenly arrived on the scene.
Police said examination of CCTV footage showed the dog had been left unattended in the car for about six hours.
They urged pet owners to not leave animals unattended in vehicles for long periods and to provide water and make sure windows were low enough to allow ventilation.
Police inquiries into the matter are continuing.