A diver off the coast of South Australia has captured the incredible moment a great white shark leapt from the waves to attack one of its fellow species.

The amazing vision was filmed by English-born Sydneysider Adam Malski last month during a diving trip off the Neptune Islands.

The 33-year-old watched in awe as a shark around 2.6m long chomped on a piece of bait attached to the side of the boat when the unexpected act of cannibalism occurred.

Suddenly a second shark at least twice the size of the first launches itself out of the water and sinks its razor sharp rows of teeth into its unsuspecting victim.

The passengers on the boat scream as the larger shark takes its smaller brethren below the surface of the water, its tail thrashing back and forth as it disappears below the white wash.

It is unclear if the shark intended to attack or if the smaller fish just happened to make the potentially fatal mistake of getting between the predator and its food.

"The day where the shark attacked the other was surreal," Mr Malski said.

"I asked the dive master and skipper of the boat what would happen if a smaller shark got in the way of a larger shark.

"The skipper responded, 'the big shark would take the smaller one down'.

"Literally six seconds later, that amazing scene was witnessed by me, the skipper and the dive master.

"They had never seen anything like it before.

The larger shark, which the group named Gilbert has since been spotted around the Neptune Islands while its victim has not.

Source: Barcroft