A man was allegedly kicked in the face and knocked out in West Auckland after his dog accidentally bumped into a child.
The man had been walking his dog along Kakamatua Beach last Sunday when it knocked the child over, a police spokeswoman said.
A man who was with the child then came up and kicked the dog walker in the face, allegedly knocking him unconscious, she said.
The man was taken to hospital with serious injuries to his face.
A Facebook user later made a post in a West Auckland group saying the dog had been running along the beach when "a young lad of about 10 ran across the path of the dog and was knocked over".
The user said the boy was helped to his feet and as the dog owner was putting the lead on his pet, the boy's "cowardly" father kicked him in the face and left him unconscious in the water.
Kakamatua Inlet is considered one of the best dog beaches in Auckland.
Dogs are allowed off leash at the beach apart from when walking through forested areas to prevent them roaming off track.
Police are yet to locate the attacker.
They urged anyone with information to call Waitemata Police on 09-839 0600 or Crimestoppers on 0800 555 111.