Counties Manukau senior sergeant Jeremy Field said the behaviour was unacceptable.
"This sort of behaviour is not tolerated in the community," he said.
"Everyone who attends sporting events like this needs to be safe and feel safe while attending."
He said it was unclear whether any charges will be laid and that the investigation was ongoing.
Mr Field was unaware of any previous tension between the teams and said both schools were co-operating with police enquiries so far, he said.
He added that it was not clear whether school rugby brawls were becoming a trend.
Two weeks ago, and 11-year-old boy allegedly punched a referee after tackling him to the ground during an under-12 rugby game in Papatoetoe.
The incident happened about 10 minutes into the second half of a rugby game at the Papatoetoe Sports Grounds.
The child could face a lifetime ban from the sport.
A spectator at the game who called in to Veitchy on Sport said it was "complete chaos".
The fight started after a Tangaroa player charged an Otahuhu player, he said.
Parents got involved, with some hitting students with umbrellas, he said.
"They threw a couple of punches and pushing each other and then from how I understand it a relative from the Tangaroa student, 'cause the fight took place where the Tangaroa supporters were, and he just threw a punch into the back of the Otahuhu student's head and knocked him completely out cold," the man said.
"It's just shocking, watching everything unfold. A referee got between everyone and stopped it, and sent everyone off to their sides," he said
