A killer whale has washed up on a West Auckland beach with suspected blunt force trauma to the head.

The adult male, found on Whatipu Beach, was possibly hit by a boat.

"At this stage it's too early to speculate what the cause of the trauma may be, although boat strike is an obvious consideration," Coastal-Marine Research Group director Karen Stockin told Fairfax.

The beaching has been reported to the Department of Conservation (DoC), which asked permission from local iwi to start an autopsy.

A team from Auckland's Massey University will also be examining the mammal, with the aim of taking a biological sampling to assess its diet and pollution loads on Tuesday.

Killer whales are considered nationally critical in New Zealand and their known threats include fisheries interaction and boat strike, and anyone who accidentally kills or injuries a marine mammal has to report the incident to DoC or a fishery officer within 48 hours.

A vessel travelling over five knots could cause severe damage to a whale or a dolphin, but travelling above 15 knots would result in a likely death.

Newshub.