A dog owner walked away after his Staffordshire bull terrier attacked a four-year-old boy, leaving him with serious injuries to his face.
Police described the man's actions as "staggering" and said the young victim required plastic surgery and may be scarred for life.
The child was bitten as he walked with his mother and siblings along a footpath near Tilehurst Place in Blurton, Stoke-on-Trent, at about 12.30 pm on Sunday.
Sergeant Andrew Bryan, of the Stoke South Local Policing Team, said: "We are keen to trace the dog and its owner as soon as possible.
"The fact the owner walked off without offering to help the boy and his mother is staggering. We need to find this dog quickly so we can prevent it biting other innocent people."
The owner, whose brown terrier was not on a lead, is described as white, in his late teens or early 20s, and was wearing black trainers, grey tracksuit bottoms and a black hoodie or coat.