A heavily armed police officer stormed a swimming club in the middle of a race last night - scaring children and making them stand against a wall.

About 50 children and parents at Papamoa Swimming Club were unwittingly caught up in the middle of an armed offenders squad (AOS) callout.

Children cried when a masked AOS officer entered the pool area and ordered them up against the wall at 7.20pm.

A man understood to have access to military style weapons and deteriorating mental health was inside apartments opposite the pool centre in Parton Rd.

The area was cordoned from Papamoa Beach Rd, Dickson Rd and Tara Rd.

Ms Raubenheimer said the children were initially scared, especially the ones who did not have parents with them. However, other parents looked after them.

The incident lasted about 35 minutes. The man was arrested but later released following a mental assessment. Several guns were seized.

The AOS member returned to the upset children and took off his balaclava and mask to show them he was no monster.

Kym Raubenheimer, one of the parents at the pool, said the officer told the children he was there to keep them safe and they didn't need to be afraid of him.

"He was absolutely marvellous," she said.