A woman had part of her top lip bitten off by an unknown man at Notting Hill Carnival who told her he was “the devil”, police said.
The woman, who does not want to be identified, was on Portobello Road near Golborne Road when he leant forward and bit her.
She has been left with life-changing injuries and will need “extensive surgery”, an officer added.
The attack happened on the first day of carnival – 25 August – at 18:00 BST.
The suspect has been described as a black man with short black hair and of muscular build. He was wearing a black T-shirt.
Officers have appealed for anyone who may have witnessed what happened to come forward.
Det Ch Insp Hayoukane said: “This was a horrific incident on a woman who has suffered life-changing injuries, requiring extensive surgery.
“The man who did this is clearly a violent and dangerous individual and I am determined that we identify and apprehend him as soon as possible.”