Amateur video of what is believed to be a killer whale attacking a group of sharks in the surf has been shown on New Zealand television.

The attack occurred at Tuatapere's Blue Cliffs beach, which is popular for fishing and swimming, on Tuesday.

It is thought the killer whale may have been herding the sharks towards the beach.

Eyewitness David Evans said he was told there were whales in the area - so he headed down to the beach with a camera.