Giants of the sea: Blue whales spotted in NZ

They're some of the planet's most elusive creatures - but they're taking a tour of NZ right now.

Rare blue whales have been spotted off the coast of the North Island by NIWA scientists.

The whales, the world's largest animal remain one of the planet's most elusive creatures.

They were intensively hunted in the Southern Hemisphere during the whaling era, dramatically reducing their numbers.

The creatures were spotted by scientists on a research expedition in the South Taranaki Bight led by NIWA marine ecologist Dr Leigh Torres.

Thar she blows! Deb Glasgow took this photo of a blue whale feeding off the South Taranaki Bight.

The group is aiming to collect data to increase understanding of the blue whale population in the region. The team has observed nearly 50 blue whales in the past week.

"It is very exciting to see these whales and start the process of collecting important data on this undescribed population and poorly understood foraging habitat,'' Dr Torres said.

"In addition to finding the whales, we were able to detect their prey visually on the surface and at-depth using hydro-acoustics.''

Dr Torres last year published a scientific paper that discussed the possibility of a blue whale foraging ground in the Bight.

Her research showed the presence of blue whales in the area was greater than expected. An increase in reported sightings was also linked to a prominent upwelling system that generates large clouds of plankton - perfect for blue whales to feed on.

It was previously thought the whales were only travelling through New Zealand waters while migrating.

"Blue whales need to eat vast amounts of plankton to support their energy demands. But there are just four confirmed blue whale foraging grounds in the Southern Hemisphere outside of Antarctic waters,'' Dr Torres said.