In most cases, a person must have been missing for seven years before they can be declared legally dead, which is a decision a High Court judge makes after examining all the evidence relating to the disappearance.
But a coroner has the power to declare a person dead earlier.
In a missing-person case like that of Kaye Stewart, once police have exhausted all their avenues of investigation and believe the person is dead, they can refer the case to the coroner for a ruling.
If the coroner is satisfied that it is likely the missing person is dead and their body is destroyed, lost or cannot be recovered, an inquest will beheld.
"They will need evidence that the missing person is probably dead, like the circumstances of their disappearance, bank accounts have stayed unused since the person went missing, or there has been no contact with family, friends or work colleagues," the Ministry of Justice website explains.
"If the coroner concludes that the missing person is dead, the death can be registered by the coroner with Births, Deaths and Marriages. A death certificate can then be issued. In some cases, it may be necessary to make a finding where a body has not been able to be recovered but its whereabouts is known. In these cases evidence of the fact of death still needs to be established."
Joanne Chatfield, 17, disappeared in Auckland after leaving a function at Auckland University just before midnight on November 18, 1988. Coroner Murray Jamieson declared her dead, presumed murdered, in 2008.
Ronald Alfred Oldham, 9, was last seen playing alone at the Miramar Wharf in Wellington on the evening of February 17, 1941. Police believed Ronnie fell from the wharf, hit his head and drowned, but his body was never found. In 2009, Ronnie was officially declared dead by coroner Garry Evans.
Mother of one Kelly Fitzgerald disappeared at Tikitapu in August 2009. In 2011, coroner Wallace Bain declared she was dead, presumed drowned, after apparently taking her own life.
Iraena Asher disappeared at Piha in 2004. In June last year, coroner Peter Ryan ruled that she was dead, presumed accidentally drowned.
Missing in NZ
• Each year, police receive more than 8000 reports of missing people.
• Of those reported missing, 95 per cent are found in a short time, usually within two weeks. More than half are found within two days of being reported missing.
• But police records show more than 300 people who have been missing for more than one year.
• They may be missing by choice, they may have wandered off or be evading police, they may have committed suicide, or they could have disappeared against their will through crime or misadventure.