Creature from the deep: Most likely the rotting carcass of a killer whale. Photo: YouTube

A video of a "sea monster" that washed up on a New Zealand beach has gone viral despite experts saying the mysterious creature is probably a killer whale.

The rotting carcass washed ashore on a beach east of Tauranga in stormy weather late last month.

A Pukehina Beach resident, with the YouTube profile Elizabeth Ann, filmed the creature and posted the video asking for any suggestions about what it was.

<i>Illustration: Cathy Wilcox</i>

Illustration: Cathy Wilcox

"It has a huge head and teeth with rudimentary flippers," she said.

"It seems about nine metres in length but the lower part of the body is probably mainly entrails from an attack."

The video has gained more than a million views, which could largely be due to over-excited elements of the British media which have labelled the creature a "prehistoric sea monster".

"A close-up of the creature's gaping mouth shows its fearsome jagged teeth," wrote the Daily Mail.

Tabloid The Sun speculated the "beast from the deep" could be a a killer whale, a "saltwater crocodile, giant moray eel, some sort of dolphin, or something more prehistoric".

International science journal Nature World News said creatures that washed up on the shore were often badly decomposed, so much so that they bore no resemblance to any known animals.

The Discovery Channel said New Zealand was one of the most common places, along with Newfoundland and Florida, for such "sea monsters" to appear.

A marine mammal expert from the Museum of New Zealand, Anton van Helden, told NZ media that based on the creature's fins, it was most likely to be a killer whale. The body had probably been floating around at sea for some time before it washed up, he said.

"It is very typical for whales of different shapes and sizes to wash up on beaches around New Zealand."

The remains have since washed out to sea.

Fairfax NZ