Incredible koru-like clouds blanket Palmerston North sky

Palmerston North residents have been treated to an unusual sight in the sky.

Bizarre cloud formations, known as "breaking wave clouds", formed above the city on Sunday morning and were captured by Carl Gadsby in a picture posted by MetService.

The formation is very rare and requires a number of atmospheric conditions to form.

"They can occur whenever the wind and air density change fast enough, as found near a jetstream - a river of rapid moving air aloft," the MetService website says.

MetService forecaster Tuporo Marsters said it was the first time he's seen the phenomenon over the Tararuas, as it is more common at high altitudes.

"There must have been something that formed the first wave and then it protruded down the track."

The strange sight has left social media amazed.