A rare and massive black marlin has been discovered washed up on a Canterbury beach, stunning an early morning walker who came across the extraordinary sight just after dawn.

Christchurch resident Jack Stewart has come across the fish at about 5am while walking along Kaitorete Spit, south of Birdlings Flat.

Stewart said the marlin was enormous, measuring about 3 metres from its eyes to the base of its tail, not including its bill or the widest part of the tail.

“I am 6ft2 laying beside it,” Stewart said.

“Just in awe of the size really, first time I had seen a marlin other than TV and it was just so impressive.”

Stewart believed the fish may have come ashore during the high tide at about 3am.

“Being told its unheard of in these parts to see a black marlin,” he said.

“Water generally too cold down here for them.”

Photos shared with chrislynchmedia.com showed the huge fish lying on the sand, with Stewart pictured beside it to give a sense of scale.

Black marlin are usually found in warmer waters and are rarely seen so far south, making the discovery an unusual sight for the Canterbury coastline.