An Auckland couple has had an unexpected yet incredible encounter with a giant humpback whale on Auckland's Hauraki Gulf.

On Tuesday, Josh and Jo Western were out at sea fishing for snapper when suddenly a giant humpback whale burst out of the water, coming inches away from their boat.

Josh, who teaches people how to use fish finders, told the Herald the whale gave him a "hell of a fright" but says it was one of the coolest experiences of his life.

"It was pretty cool. But it was as close as you want to get.

"We'd seen it from about 200m away. It was in an area that was quite tidal, an area where I'd suspect a whale would have a high risk of getting stranded. It was completely out of character for a humpback to be in that area and out of the migration cycle.

"He was about 100m away and he dropped under the water and we lost track of him. Then all of a sudden he popped up beside the boat and launched himself out of the water. He was so close we could have reached out and touched him."

Josh estimated the whale to be 12 metres long, about twice the length of his boat.

The couple called the Department of Conservation to alert them to the whale, telling them it was swimming in shallow, 2-3 metre waters.

Not wanting to cause trouble, Josh kept his boat between the whale and the shoreline, to avoid pushing the whale towards the coastline.

The curious whale then came closer to the boat, wanting a good look at Josh and Jo.

It came back for one big splash before curiously hanging out with the couple for about two hours.

"We sat with him for about two hours with the boat turned off," Josh said.

"I'll spend 20-30 hours a week on the water. I've swum with dolphins more times than I can remember and swam with orca whales and Maui dolphins but this probably the coolest in terms of getting so close to such a big creature."

Jo, who is a photographer, captured the footage and uploaded it to Facebook.

It has been viewed more than 12,000 times.

Josh explained the sighting at this time of year is extremely rare, especially along the east coast.

"It must have been geographically challenged," Josh joked.