Police in the Far North have arrested a 15-year-old girl after what they call a prolonged assault at a bus depot, with video of the attack circulated on-line.
They say the attack happened in Kaikohe on Tuesday.
The victim, a schoolgirl, suffered injuries to her face and head, and she and her family are upset and shaken.
Police said a video of the attack was widely circulated on-line - and sharing it indicated an acceptance of thuggish behaviour and glorification of the offender.
Senior Sergeant Brian Swann said the prolonged and vicious assault ended when adults intervened.
"A person who knew the victim walked up and told the offender to stop, but was threatened himself, she then carried on the assault and another adult intervened."
Mr Swann said sharing the video indicated an acceptance of thuggish behaviour and glorification of the offender.
They have charged the 15-year-old with assault and she was due to appear in Youth Court today.
Police were also investigating the roles of people who encouraged and aided the offender.