A man who surfaced from a dive at Matapia Island near Ninety Mile Beach died at the scene despite efforts to revive him.
The incident happened about 11am on Saturday.
A police spokeswoman said the diver was found unconscious and was given first aid but the 47-year-old man died.
Emergency services, including Search and Rescue were at the scene.
The death will be referred to the coroner.
The Te Aupōuri kaumātua on Saturday placed a rāhui from Waipakaru to Te Paki Stream for three days.
In a separate incident, another diver reported missing in Cape Reinga on Saturday has been found alive and well.
The man was reported missing about 3pm after failing to surface near Three Kings Islands.
An extensive search and rescue operation was launched alongside Coastguard, and the diver was located on rocks by a charter vessel about 9.15am today.
He was transferred to a second vessel and returned to Whangaroa.
The search involved the Navy, Air Force and Army. An Orion was deployed in the area this morning along with the Northland Rescue Helicopter.
Charter operators and Far North radio used their experience and vessel communication to successfully locate the diver.