In the clip, you see a pair of dorsal fins rip through the ocean at pace as they head towards the kids.

The children panic and cling on to each other for dear life.

You also hear them scream as they believe they are about to be devoured by the predators, which can measure up to 8 metres in length and weigh up to 6 tons.

“That's a lifetime experience for you,” one onlooker could be heard saying as the two orcas swam past the children and back out to sea.

The clip was recorded in waters off Waiheke Islands in New Zealand earlier this week.

One witness, Shane Watt, told 1 News: "The kids were obviously very, very frightened.

"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."

Uploaded to Reddit earlier today, it has caused a mass reaction from viewers.

One comment read: "It's crazy how effortlessly and quickly they overtake the swimmers at what looked like half speed.

"Can't imagine that s*** barreling at me looking to kill."

And another added: “Oh my God, they are so lucky.”

Orcas are also known as killer whales.

They get their name from being at the top of the sea-life food chain.

Although they are not known for attacking humans, there have been reported cases of fatal encounters.