An off-duty police officer who saved the lives of three girls saw a look of terror on one of their faces, just before she went back under the water.

The dramatic rescue happened on Sunday at Rotorua's Lake Okareka about 3pm, where Dannervirke-based Senior Constable Wayne Churchouse was holidaying with his two sons.

He says he was on a paddleboard and returning to shore when he first saw the three girls, who he believed were aged between 7 and 9.

"I had a glance and thought they were just playing," he says.

He took a second glance – an act that helped save their lives as he saw they had all gone under the water where the lake bottom drops off steeply.

Wayne describes seeing the girls "climbing on each other" as they tried to reach the surface.

He also describes the moment he knew it was serious.

"I could see terror in her face as she gasped for air, and she said 'help'."

He says he jumped off the paddleboard, grabbed the girls and pulled them to shore – just 20 metres away.

Remarkably, he says the incident happened when the beach was "packed".

"There were people all around," he says.

"It could quite easily have been a tragedy. They were just pushing each other. . . They knew they were in trouble."

He says that after reaching the shore, the girls coughed a little but were physically fine. They thanked him then ran off into the crowd.

"I was just lucky to be at the right place at the right time," he says.

"You do what you've got to do."

Wayne says his police training proved critical as he is always alert – and he's a strong swimmer.

He says that when it came to being around water, "everyone needs to be vigilant, especially of children".

He says even strong swimmers can get into trouble, especially when panic sets in.

"They'll try and climb on anything to keep their head above water."

-Stuff