A white porpoise has been spotted off the coast of Cornwall.

The very rare mammal - known as a leucistic porpoise - was captured by Marine Discovery in Mount's Bay, off Penzance.

It's colouring is due to a condition which means it's experienced a partial loss of pigmentation resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticle, but not the eyes.

It's not known whether it is the same porpoise spotted off the north Cornish coast in 2016.

The harbour porpoise species have dark grey or brown colouring with a white belly.

Credit: Twitter / @Marine_Discover

There are currently around six known species of porpoises in existence today, according to Whale Facts.

Credit: Twitter / @Marine_Discover

Porpoises also typically grow between five to eight feet long and weigh between 100 and 200lbs, with the larger porpoises weighing over 400lbs.