A group of divers on the Lower Eyre Peninsula say they saw a pod of killer whales single out and kill a great white shark.

They came across the family group of orcas, including two calves, during a shark-cage diving trip at Neptune Islands near Port Lincoln.

Matt Waller from a local charter company said he's never seen anything like it before.

"You're looking at the two apex predators of the marine world- it's like the title fight of all title fights."

Those who witnessed the attack said it was an unbelievable and emotional sight.

"It was really weird, people were crying, people were laughing, people were swearing, they were at the height of emotion," Mr Waller said.

Mr Waller said the attack involved a family of six killer whales, including two calves.

"These whales were working, launching themselves out of the water and slamming down on top of the great white shark.

"I can only imagine if that's what we were seeing on the surface, that under the surface you had other whales which were working to try and keep this shark up.

"It never actually went down it stayed on the surface and was trying to get away."

Whale expert and Senior Researcher at the South Australian Museum, Dr Catherine Kemper, said while she has not heard of this having occurred in South Australia before, she will confer with international colleagues to find out more about orca behaviour.