A pod of three killer whales attacked a humpback whale mother and her calf off the coast of Ningaloo in Western Australia on Friday, in a phenomenon rarely seen by scientists, but captured on film on this occasion.

Drone footage filmed by two fisherman and obtained by Reuters showed the humpback whale mother and her calf initially fending off a synchonised attack from the three killer whales.

However, the orcas eventually managed to kill the calf.

"I was marlin fishing and had the first orca shoot in and roll right under the boat, showing off and playing," said Shane Stephen, one of the fishermen who witnessed the attack.

"Shortly after, we saw splashing and a commotion and knew a hunt was under way. It is the first orca hunt and kill of a humpback whale this season and went on for almost two hours."

Stephen told Reuters that the humpback mother's calf was "taken" and separated from the mother after two hours.

Orcas hunt in groups, and their prey includes fish, cephalopods, whales and sea turtles.