Bay of Plenty residents were treated to a jaw-dropping sight this evening as a cold southerly set in over the eastern North Island region.

No, it wasn't snow but rather strange-looking UFO-like clouds - also known as lenticular clouds.

The lens-shaped wave clouds form when the air is stable and winds blow across hills or mountains from the same direction at different heights.

WeatherWatch.co.nz says fading southerly conditions and cooling temperatures helped produce the cloud, which dumbfounded some locals.

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Lenticular clouds are common over parts of Canterbury because of the Southern Alps and nor'westers connecting.

The lenticular cloud over Bay of Plenty tonight:

In 2016, a lenticular cloud sparked panic in Northland after it was mistaken for an "alien spaceship trying to enter the atmosphere".

Hovering off Ruakaka Beach, the oval cloud was pink and initially locals believed it was the ship's red-hot hull.

At the time, MetService meteorologist Lisa Murray said the clouds were often associated with spaceships because of their smooth edges.

There needs to be enough moisture in the air for the wind to make sure the waves condense to form lenticular clouds, Murray said.

The lenticular cloud in 2016 over Northland. Photo / File
The lenticular cloud in 2016 over Northland. Photo / File