Emergency services were called to a water rescue near Jacks Bay Rd about 1pm today.
A witness who saw the event unfold said a group was snorkelling off the shore of Tuhawaika Island when one person appeared to need medical attention.
Emergency services arrived and went over to the island on boat and performed CPR on the person for over 45 minutes.
A rescue helicopter landed on the island, but it appeared to be too late, he said.
Another person was in the area during the aftermath and captured footage showing a deceased person being taken away from the scene.
A police spokesman said it attended a water rescue with Fire and Emergency New Zealand and St John, but were unable to provide further comment.
A St John spokesman said one helicopter arrived at the scene, but was not required for transportation.
