There is a significant police presence at Onerahi's Beach Road, the area is dotted with emergency services vehicles, and police are enforcing a cordon around what is believed to be a shooting at the reserve.
Police said they received reports of a person injured at Beach Road Reserve about 11am on Thursday.
"Upon arrival, one person was pronounced deceased at the scene," they said in a statement.
"A second person was located with serious injuries and has been transported to hospital."
People have been warned to avoid the area.
Locals said the incident involved a man and a woman, and that the woman had died.
Armed police at the scene are turning people away, including residents trying to get home. The cordons on busy Beach Road are from Church Road onwards.
People leaving the cordoned area are being questioned by police and some have reported seeing and hearing guns.
St John said it had sent three ambulances, a rapid response vehicle and an operations manager to the scene, and one patient was taken to Northland Base hospital in a critical condition.
Just before 2pm on Thursday, acting detective senior sergeant Shane Pilmer said police did not believe there was any risk to the wider community, but police want to hear from anyone who saw the incident.
"The key focus for us is determining the series of events that led up to this tragic incident."
A scene examination was now being carried out.
Cyclists trying to do the popular route around the headland are being turned away and told the cordon may remain in place for some time.
Although police had visited nearby Raurimu Avenue School, it was operating as normal.
Anyone with information about the incident was asked to call Police on 105, or to visit their Update Report page online at 105.police.govt.nz and quote file number P061751387. Information could also be provided anonymously through Crimestoppers on 0800 555 111, or on their website.
