Shark didn't eat body's missing leg - police

A man's body, found off Auckland's North Shore with a leg missing, is believed to be that of a missing swimmer.

Police say it's not yet clear how the man died, but have ruled out a shark being involved.

Ports of Auckland chief executive Tony Gibson, in a statement, has confirmed one of the company's boats was under police investigation over the man's death.

The circumstances were not clear, but they were cooperating fully with police.

"I am extremely upset that one of our pilot boats may have been involved in the death of a swimmer," Mr Gibson said.

"I understand the pain this will have caused and I offer the family and friends of the swimmer my deepest sympathies for their tragic loss."

On Thursday a search was launched after a man failed to return from a regular swim off Narrow Neck Beach.

The body was spotted by passengers on a commuter ferry on Friday. "It was a very distressing mental image," one witness told NZME.

The witness said the man was wearing a wetsuit, and the right leg was missing up to his waist.

The witness told the paper he thought the swimmer might be the victim of a shark attack because his right leg was missing up to his waist, but police think that is unlikely.

The man's name is not expected to be released until relatives overseas have been informed.

NZN / Newshub.