A video has emerged that appears to show a police dog bite a man on the neck as he moves to stand up in front of it.
This brief clip, filmed by an onlooker, shows the dog's handler trying to restrain it as it barks at the shirtless man on a street in Weston-Super-Mare, Somerset, who moves to stand to get away from it.
But as he does, the dog manages to lunge forward and appears to grab hold of his neck and and does not let go, despite two officers trying to get it off.
A witness can be heard saying: "Oh my god, it's biting his head."
Avon & Somerset Police's Assistant Chief Constable Louisa Rolfe told the BBC that the incident was subject to an internal investigation.
She said: "During this incident, a man was bitten by a police dog as he was being arrested.
“We are aware of a YouTube clip and comments on social media channels about this incident.
“The incident has been referred to our Professional Standards Department for thorough investigation as we are keen to understand what happened.
“The YouTube clip is only a few seconds long and doesn’t show events before or after the arrest.”
The Bristol Post reported police were called to the scene after a large fight.