Police are appealing for a couple in their mid-thirties who saw a woman in a distressed state on the Mercer Bay loop track at Piha on Saturday night, to contact them urgently.
A land-based search for the woman was called off on Sunday, however police hold grave fears for her safety and a search of the ocean will continue at first light on Monday.
The woman's car was found unlocked at the carpark near the Mercer Bay track.
The couple went to a nearby house and alerted the police and then left the area.
Sergeant Dene Duthy says the police hold grave fears for the woman and need to speak to the couple who saw her on the track at about 6.40pm on Saturday.
He says the couple spoke to a person at a house who then called the police.
Sergeant Duthy says the couple have done the right thing by alerting the police and it's important they now come forward.
Police have not given any details about the woman.