A dog owner is distraught after finding her beloved pooch dead in the boot of a locked car in Sydney’s east after receiving a text message from her dog walker six hours later.

The emotional woman, 46, was hoping for the best when she went to Rose Bay to rescue her four-year-old Keeshond at 5.30pm on Tuesday after the dog was not returned home.

Since 11am, the dog had been left unattended in the locked-up vehicle, owned by Signal Station Dog Walking.

“I’m really sorry, I think I left your dog in my car,” the dog walker said via text message to the owner.

Glenn Herne smashed the window of this car to rescue the dog which was trapped inside for six hours. (Supplied)

Passer-by Glenn Herne, 33, was returning home with groceries when the woman abruptly approached him for help on the street.

“She came over very upset and said she thought her dog was locked in a car,” Mr Herne said.

“I couldn’t see the dog because the car had tinted windows. The woman was hysterical and in tears. She was inconsolable.

“I started tapping on the window to see if there was any movement but there was nothing.

The dog that died was a four-year-old Keeshond, similar to this pictured above. Picture: Facebook

“I went to my ute and got a lump hammer to smash the back left window. There was a mesh screen in the way but I eventually got to the dog in the boot and tried to wake the dog up.

“He was rigid and still as a plank. His fur came out in my hand when I lifted him up. He was falling apart. The car was very small, warm and smelly so I put him on the grass.”

Mr Herne, an electrician, said the dog’s owner kept her distance but repeatedly asked if her canine had died.

“There was a towel in the car which I put over the dog and then neighbours came out and asked if it was a child,” he said.

A map showing the location where the dog was found locked in a car. (Google Maps)

It is believed the dog walker left the dog in the car after embarking on a cruise.

“How could you be so careless to just hop on a cruise?” Mr Herne questioned.

“It’s ridiculous. I don’t know how you could forget. This woman is supposed to be a dog lover. You could tell by the way she parked her car that she was in a rush.”

The RSPCA has been notified and the incident is being investigated by police.

Police are urging the public that not only is it an offence for children or pets to be left unattended in a vehicle, even with the air-conditioning on, but it can be deadly, especially during the heatwave this week.

Temperatures in parts of New South Wales and southwest Queensland are hitting more than 40 degrees today with the severe weather not expected to ease until mid-next week.

Anyone who finds a child or pet located in a vehicle are urged to call Triple Zero (000).