Rare blue whale footage captured in New Zealand

The mammals were sighted by staff researching pygmy blue whales in the region. Photo / YouTube - National Geographic

Rare footage has been captured of a blue whale nursing its calf in New Zealand waters.

National Geographic has released the video, recorded by a group of researchers working in the South Taranaki Bight early last month.

The mammals were sighted by staff researching pygmy blue whales in the region.

When they spotted what appeared to be a mother and her calf, they kept their distance and sent up a drone to record some footage and take photos.

National Geographic explorer and marine ecologist Leigh Torres said they could see the smaller mammal going under its mother for some time before returning to the surface -- and repeating the process.

"We had no idea they were [probably nursing] when we saw them from the vessel. But from the overhead perspective, we could clearly see this co-ordinated behaviour between mother and calf," she said.

"It was beautiful to see."

The footage is thought to be the first time the rare event has been captured on video.