A criminal investigation is under way after a dog had to be euthanised due to serious injuries it suffered during an alleged attack outside a NSW shopping centre.

The dog’s owner tied the rottweiler up to a tree on Steel St in Newcastle West before going inside a nearby shopping centre about 12pm on Friday, according to police.

When he returned 15 minutes later, the dog was suffering from serious injuries.

It is believed that while the owner was inside the shopping centre, a group of people assaulted the dog and caused the injuries.

The man took the dog to a vet, however its injuries were too serious and the dog had to be euthanised.

As a result of the alleged circumstances surrounding the incident, police established a crime scene and have commenced an investigation.

They are appealing to anyone in the public with information on the alleged attack on the dog to come forward.

Police are urging people who witnessed the incident to contact Crime Stoppers on 1800 333 000.