One schoolboy was bashed unconscious and another left with broken teeth after they were allegedly attacked by a 17-year-old.

A police officer found the the two brothers, aged 11 and 12, bleeding at 1am yesterday following the attack.

Senior Sergeant Warwick Burr said police were still investigating the lead-up to the incident, but it appeared the boys were walking along the street with two other primary school-aged boys at the time.

As they passed a Bannister St property they were allegedly approached and attacked by a 17-year-old.

A call from a neighbour alerted police, Burr said.

Two of the boys managed to avoid the altercation, while the brothers received moderate injuries along with minor cuts and bruises.

They were taken to Wairarapa Hospital, where they were treated and later discharged.

Burr said police later arrested the 17-year-old, charging him with assault with a weapon.

He is due to appear at Masterton District Court today.

It is not known why the boys were walking through Masterton at that time of the night.

An investigation into the incident was continuing, Burr said.

- © Fairfax NZ News