A large adult sperm whale is believed to have got itself back over the Raglan bar.

The male, estimated at 10 to 15 metres long, was seen lolling about in the Raglan Harbour most of Thursday.

It was initially thought to be injured or sick.

JO BOURGEOIS/XPOSURE PHOTOGRAPHY Raglan Kayak and Paddleboard owner Stephen Reid kept his distance but said the encounter was emotional.

Ingrid Visser, a researcher with the Orca Research Trust, said that while the whale had been identified by its markings as male, it wasn't known why it entered the harbour.

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"It may be as simple as him being curious or it may be that there was something wrong with him. But he has been swimming out of the harbour and we believe he's gone over the bar and is in the ocean at the moment," Visser said.

JO BOURGEOIS/XPOSURE PHOTOGRAPHY More paddleboarders get a closer look.

Adult male sperm whales are typically quiet, solitary mammals.

This is the same species found off Kaikoura, where there is a collection of them. However, they are not socialising but hunting for food in the rich environment there.

"The Raglan whale wouldn't be feeding in the harbour," Visser said. "They feed predominantly on deep-water species like squid and some of the deep-water sharks."

ARNE KAMINSKY/SUPPLIED Witnesses said the whale appeared to be unwell.

The Department of Conservation and the Raglan harbourmaster responded to the sighting about 8am. Initially it was feared it might beach on Wainamu Beach, off Riria Kereopa Memorial Drive.

Raglan Kayak and Paddleboard owner Stephen Reid was flabbergasted when a friend phoned to tell him about the whale.

He raced down to his rental business and headed straight out on his paddleboard.

ARNE KAMINSKY/SUPPLIED Paddeboarders head towards the whale.

The whale looked sick, he thought.

"I was with it by myself for a while," he said after getting back to shore. "It was pretty emotional.

"It looked like it was just drifting. It never dived down, but would pop its head up now and then and blow its spout."

Reid kept his distance, staying around 100 metres away.

"It was amazing, I felt very small in the water next to it."

He enjoyed 15 minutes alone with it before others arrived on paddleboards and kayaks.

"At that stage people were getting really close, and it felt a little bit intimidating for the whale.

"A lot of people had the same feeling - that it wasn't feeling well."

Locals came out to sing a waiata or say a karakia, Reid said.

One local who declined to give her name said she had lived in Raglan for 30 years and had never seen such a large whale in the harbour.

"It was beautiful to see all the local people who came out and on to the shore. They were singing Māori to the whale and it was so special to see that local vibe."

Murray Page, 76, spotted the dark shape from his home on the Te Akau side of the harbour shortly after noon on Thursday.

"I saw some boats going out to the brown thing in the water, so I grabbed my binoculars," he said.

"It looked like a cow at first."

Page has lived in the seaside town for the past 10 years and has owned a bach there for 38.

There have been numerous orca sightings, but Page had never seen a sperm whale before.

He said the mammal got within 100m of the Raglan wharf just before 1pm.