Police have said a street fight in central Wanganui on Wednesday night was over opposing gang colours.
A 16-year-old from Auckland was stabbed and bashed in the incident. He remains in a critical condition in Wellington Hospital.
The teenager was stabbed in the face and bashed across the back of the head, and is in the hospital's intensive care unit after initially being taken to Wanganui Hospital.
The assault took place on the corner of Keith St and Glasgow St about 7.45pm.
Whanganui police Detective Senior Sergeant Dave Kirby said police were looking for a male Maori, 1.83 metres (6ft) tall, with a number one haircut. He is believed to have had a beige pitbull with him.
Police are still trying to piece together what happened and what caused the teen's injuries.
A woman approached the Chronicle yesterday to say the 16-year-old was on holiday in Wanganui from Auckland. He was staying at an older sister's house in Campbell St with his brother.
The woman is the partner of the older brother. She did not wish to identify herself or the brothers but wanted to explain what had happened.
She said there had been an earlier incident between the older brother and a "man in red".
Later the 16-year-old was riding around on his bike and was attacked from behind by the man, she said.
"He was bashed across the back of the head then stabbed in the face."
She said the whole episode was about "colours".
"Look it's so stupid. The older brother wears a yellow hat [Tribesmen] and the 16-year-old was wearing a blue hat, which means he associates with Black Power."
On Thursday, the brothers' family from Auckland had driven straight down to Wellington Hospital, she said. "He's pretty bad ... we know that's why they sent him through to Wellington."
A 21-year-old was arrested at the scene of the incident and is in custody at Whanganui Prison. He is due to appear in court on December 11.