Watch: Kiwi freediver William Trubridge swims with humpback whales in Hawaii

Freediver William Trubridge said the experience was "other-worldly". Photo/Dean Purcell

Champion freediver William Trubridge has had a very close encounter with humpback whales in Hawaii.

The Kiwi shared a video to social media of the "beautiful, other-worldly" moment he and his girlfriend came across two enormous whales near Maui.

"We came across this pair of adult humpback whales, immobile in the water, sending their song across the Hawaiian channels. It was a beautiful, other-worldly experience, before they slowly lifted their tails and faded into the blue," he said.

In the video, Trubridge's girlfriend Sachiko Fukumoto can be seen swimming with the whales before they fade into the blue.

Trubridge said the couple were "lucky enough" to be involved with a film crew who were working to capture the birth of a humpback whale on camera for the first time.

The project was run by a group called Kohola - which means whale in Hawaiian.

The group, formed by a team of young marine naturalists, was raising money on Go Fund Me to help get them out on the water and acquire innovative technology, like underwater drones, to capture the ground-breaking footage. They have raised $8000 of their $50,000 goal so far.

"Our jobs are to spark conservation through inspiration. We take hundreds of people out on the water every day and show them why these fish, corals, whales, dolphins, and turtles are worth protecting and why this ocean is worth saving," Kohola's Go Fund Me Page read.

According to the page the National Marine Fisheries Service has granted the group a permit that allows them to get within 91 metres of the whales for the film.