The 68-year-old was in the historic Wesleyan area of Auckland's Waikumete Cemetery when he collapsed around midday.
Bystanders, including a nurse, rushed to help him and he was given CPR at 12.14pm, police said.
Emergency services were called to the cemetery, which was packed with mourners, however the man died in front of onlookers. A fire appliance carrying lifesaving medical equipment arrived two minutes later.
Senior Sergeant Michael Rickards of Waitemata Police said the man collapsed "about 12pm today while tending to his parents' gravestone. Members of the public tried to revive him but he passed away.
"He was paying his respects, cleaning their headstone, and he collapsed and he died. We're not sure how.
"There were no suspicious circumstances.
"Under circumstances where there is a sudden death and the circumstances can't be explained, it becomes a coroner's case."
Four hours later, Auckland Council, which manages the cemetery, still hadn't been notified somebody had died on Council property, despite the cemetery being so busy that even at 4pm, traffic was backed up to the Great North Road entrance.
Cemetery Manager Roscoe Webb said today's excellent weather conditions were the reason the cemetery was packed.
"The more people that come into the cemetery, the more the likelihood of this [a death occurring]."
"I guess it's not unusual in a public open space," Mr Webb said.
While Mr Webb said the site was patrolled regularly by security guards and "is pretty much on lockdown during normal operating hours," he had still not been informed of the death four hours after it occurred.
After being alerted by APNZ News, Mr Webb said he would have to attend the Henderson Police Station himself tonight to get more information from police.
The man's death has been referred to the coroner. Police have yet to notify the man's next of kin.
- Michael Botur of APNZ
