Queensland police are searching for a man who allegedly knocked an elderly woman unconscious after spitting on her when she spoke to him about why he had not picked up his dog's droppings.

Detective Senior Sergeant Ken Rogers says officers are appealing for information about the man he called a "coward" for assaulting the 68-year-old woman on the Sandgate foreshore in Brisbane's north on Tuesday.

He punched the woman twice, police say.

The man is described as being aged in his 30s, about 180cm tall and having an olive complexion.

He was seen wearing a yellow top, dark pants, no shoes and walking a grey American Staffy with a white patch.

The man was last seen running from the scene after the assault at about 7.45am.

Det Sen Sgt Rogers described the attack as "completely unwarranted" on someone who was simply walking her dog.

""The community have the right to feel safe, particularly the elderly, and shouldn't be subjected to these kind of vicious or cowardly attacks," he said.

He said the woman was no out of hospital but she suffered significant facial injuries which included a cut and a jaw injury.

He said witnesses should contact crime stoppers.