People were happily swimming and paddle-boarding in the bay the day after the incident.

Terrifying yes, in danger no.

Orca expert Poppy Halliday​ has weighed in on a frightening video showing two orca circling past two swimming children.

On Thursday afternoon, an onlooker at Waiheke Island's Enclosure Bay recorded the moment two of the giant mammals approached the children.

DIANA WORTHY/STUFFNZ The eastern end of the bay was where the Orca came in.

The video shows the kids frantically trying to swim away before clinging to each other as the orca flanked them then cruised out to sea.

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Veteran marine guide and Whale Rescue co-founder Halliday said the gripping video shows typical orca behaviour.

DIANA WORTHY/STUFFNZ Kit Doudney went out in his kayak to rescue the youngsters.

She said the two orca were bull male whales and were "probably just curious about the kids" and split past them like a group of people would pass strangers "walking down the middle of the footpath".

The animal's sonar-like echo-location senses would have picked up the children from up to 80 metres out, she said.

"Sometimes they're echo-locating, they're seeing something and that makes them curious".

1 NEWS 'Stay still! Stay still!' - onlookers called to screaming children in Waiheke Island water as two orca approached.

Closing in the mammal's reputedly "pretty good" eyesight would have confirmed no snack was to be had.

"They realised they were two little humans and just kept moving".

Orca like getting their fill from sea creatures like stingrays, not swimming kids, Halliday said.

ANDREW MACDONALD/www.wetkiwi.co From a distance orca's fins could be mistaken for shark fins. (FILE).

"There's never been an attack by orca on humans in the wild that anyone's aware of".

Nevertheless, "anyone" let alone children would have "got a hell of a fright" having the ocean predators sashay by, Halliday said.

THE VIEW FROM SHORE

SUPPLIED Orcas will chase stingray into shallows inadvertently encountering nervous people. (FILE).

The kids were obviously very, very frightened," onlooker Shane Watt told 1 News.

"We were terrified just watching. It took us a minute to calm down afterwards so I can't imagine what the adrenaline would've been like for them."

Waiheke Island resident Brett Thom was walking his dog at Enclosure Bay when he heard a woman screaming for people to get out of the water.

LAURA VAN DER LAARN Closing in on the swimming kids the orca's reputedly "pretty good" eyesight would have confirmed no snack was to be had, Poppy Halliday said (FILE).

Initially he thought they were frightened of his dog, but then looked up and saw "two big fins".

People started shouting for the children to stay still and stay calm, he said.

Two men in kayaks went out to retrieve the kids and there was a "fair bit of crying going on," but they seemed to be OK.

One of them, Kit Doudney, said he estimated the female swimmer to be between seven and nine years' old and there was a boy of around 11 or 12.

He said the kids, who were not wearing wetsuits, had been snorkeling and hadn't heard calls from the shore to get out of the water.

There were around 20 people on the beach at around 2.45pm yesterday who saw the two fins approaching from the eastern entrance to the bay, he said.

"Someone yelled 'shark, shark, shark' and around 15 people got out of the sea.

"Everyone panicked.

"It was a 'Jaws'-like situation."

Doudney and relative Peter Wichman decided to jump in their kayaks and retrieve the kids.

He said they were no further than halfway there when the orca glided past the children, who were screaming in terror.

"Ninety per cent of me knew there wouldn't be a problem, but another 10 per cent said I'd be going to pick up some bloodied mess in the water."

But the rescue went without incident.

Wichman picked up the young girl, who was 'shaking like a leaf' while Doudney made his way to the boy who had scrambled onto some rocks.

Doudney put the snorkeling gear in his kayak and persuaded the boy to hang onto the back for a tow into shore.

The children were met by a young female carer.

They later left the island with their family, according to a local source.

Orca are a common sight around the island and there were numerous sightings on January 25 at Oneroa Bay and Owhanake Bay as well as at Enclosure Bay.

Locals have been commenting on social media, saying the warm water and surfeit of stingrays has attracted the Orca into shallows.

One of the most popular spots traditionally for Orca to catch stingray is at Matiatia, in the area around the ferry terminal.

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