His buddy was able to pull him out of the water and raise the alarm with emergency services, police said in a statement last night.
"A helicopter was dispatched and CPR was performed on the unresponsive diver, but unfortunately he did not survive," police said.
"A Royal New Zealand Navy (RNZN) vessel, which was in the area at the time of the incident and provided medical assistance, transported the man to shore."
A medic from RNZN ship HMNZS Hawea worked with Auckland Westpac Helicopter crew to try save the diver, a New Zealand Defence Force spokesperson confirmed.
The patch of water surrounding the island was "one of the most dangerous" in the world, the fishermen who spoke to the Herald today said.
"All that water from the Pacific [Ocean] has to squeeze between the top of the peninsula and Great Barrier Island.
"The seafloor is just real [uneven] and rocky ... the current is just phenomenal."
Meanwhile, the diver was most likely to be chasing crayfish or targeting fish with a speargun before the incident yesterday, the fisherman said.
Police were not in a position to name the man or release any other details this afternoon, a spokeswoman said.
