He turned on the shower, climbed out the window and ran for help. (File photo)

A father has been caught hitting his child after the boy climbed out the bathroom window after the attack and went to a friend's house with blood on him.

Caine Hemiteahau Campion, 32, hit his 12-year-old twice around the head during an argument at their home in Blenheim.

Campion's partner had accused the boy of stealing her cellphone, which he denied, about 6pm on September 2.

Campion intervened in the fight and hit the boy twice around the head, a police summary of facts said.

The boy stumbled against a wall and fell, with his head hitting a door jam. His head started to bleed and Campion told him to go clean himself up.

The boy went to the bathroom, turned on the shower and climbed out the bathroom window, and ran to a friend's house for help.

His friend's mother took him to Wairau Hospital, in Blenheim, where he received a suture for a cut on his head.

Hospital staff called police who arrived and spoke to the boy. Campion arrived shortly after and was arrested.

Campion admitted hitting his son, but said he was trying to "discipline" him for having a vape machine in his school bag.

He admitted a charge of assault with intent to injure at the Blenheim District Court on Monday.

His lawyer Philip Watson said the child had been taken away by Oranga Tamariki, the Ministry for Vulnerable Children, and Campion was working to get the child back home.

Judge David Ruth referred the case to restorative justice, where Campion would try to make amends with his son, if his son was willing to participate.

He remanded Campion to October 30 for sentencing.