Divers who witnessed a family pod of killer whales kill a great white shark in South Australia say it was "the title fight of all title fights".

The divers, who were off the coast of the Lower Eyre Peninsula, said they witnessed the attack during a shark cage diving trip to the Neptune Islands on Monday.

They said it involved a family group of orcas, including two calves.

Charter operator Matt Waller said the whales were launching themselves out of the water and slamming down upon the great white.

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

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

Mr Waller said it was the first time he had seen "two apex predators of the marine world" fight.

"It's like the title fight of all title fights," he said.

"People were crying. People were laughing. People were swearing. They were at the height of emotion."

Crew member and marine biologist Gina Dickinson said the shark was eventually killed under the surface but she could see the orca pod's "movements".

"They were teaching the young, rounding it up in order to attack," she said.

"The intelligence behind it was just fantastic.

"It was definitely the highlight of my career. Not much is probably going to top this."

A first for South Australia

South Australian Museum senior researcher Catherine Kemper said she had not heard of the behaviour occurring in SA, but would confer with international colleagues to find out more about orca behaviour.

A pair of killer whales near the Neptune Islands in South Australia. ( ABC News )

Mr Waller said attacks by orcas in other places in the world had resulted in sharks dispersing "far and wide" and had the potential to destroy the cage diving season.

"We would then be waiting for fresh new sharks to rock up in the bay and engage with our customers," he said.

"We'll only know once we go down there and we see whether there are still sharks around.

"I don't know that it will affect it that badly. It's been such a good season ... there is, in my opinion, more sharks around."