A search for a missing Department of Conservation volunteer on Raoul Island will resume on Wednesday, after an aerial and boat search failed to find any sign of him.
DoC fears the man, a volunteer from overseas, was swept out to sea as he took temperature readings of the ocean from a rock on Monday.
A search helicopter arrived on Raoul Island early on Tuesday evening after making the five-and-a-half-hour journey from Auckland.
DoC's area manager for the Kermadec Islands Tim Brandenburg says it searched for the man until it was too dark to continue.
He says the missing man is a passionate conservationist who is very fit and has previous experience as a ranger.
Mr Brandenburg says the incident has taken an emotional toll on staff on the island but they are focused on trying to find their friend and workmate.
Volunteer scheme reviewed
The Department of Conservation says it will review its volunteer scheme following the man's disappearance.
The missing man is one of four volunteers on Raoul Island, about 1000km northeast of New Zealand, and has been there for two months as part of a six-month stint.
Mr Brandenburg says volunteers undergo a strict interview process and must meet criteria, such as a high level of fitness before being accepted.
He told Radio New Zealand News on Tuesday the Department of Labour has been advised of the incident.
"We are interested in our staff and our volunteers' safety - that's the No 1 concern. Obviously, if there is a way of improving that through learning from instances like this, we will implement whatever is necessary. There will be a full investigation."