Workers on remote Raoul Island are struggling with unanswered questions as hopes fade for their missing colleague, feared swept out to sea.
The Department of Conservation (DoC) volunteer went missing from the rocky shoreline of remote Kermadec island about 6am yesterday.
Ground and air searches stretching into the night failed to find the man.
He had been rostered to take water temperature readings for a weather station DoC operates for the MetService.
Some of his measuring equipment was found at the bottom of a walking track down from a cliff where he had parked his four-wheel-drive vehicle, but there was no other sign of him.
DoC spokeswoman Liz Maire this afternoon said the probability of the volunteer being found was "quite slim''.
The Rescue Coordination Centre said it considered the search an active search and rescue operation.
Ms Maire said the three workers and three volunteers remaining on the island would do all they could to find their workmate.
"Understandably they've been very emotionally involved. It's not easy to cope with an incident like this, where there's lots of unanswered questions,'' she told APNZ.
The team were taking a break from the search this afternoon as they awaited the arrival of the Taupo rescue helicopter, which has been called in to help with the search.
The helicopter left Auckland's Ardmore air base about 11.30am and was due at the island about 5.30pm.
Ms Maire said once the helicopter arrived, the team would also be able to search from the sea as well.
"The rule is that there has to be a back-up boat whenever a boat is in the water, or a back-up aircraft.
"There's only one certified skipper on the island at the moment, so we've played it safe and are waiting for this aircraft to arrive so the boat can be launched.''
Ms Maire said staff were keeping up their spirits, having kept busy with the search this morning, but were now resting.
"We're recommending that they just save their energy in case they're required to be deployed to a certain spot if anything is found. We don't want them worn out by the time the helicopter gets there.''
Taupo rescue helicopter chief pilot John Funnell said the helicopter would launch its search from Fishing Rock, where the man had gone missing.
"We'll be searching all the little islands, the coastal lines and rocky outcrops to see if we can find the missing party.''
It was hoped the helicopter could start searching from about 6.30pm today.
It would search for the remaining 90 minutes of daylight and resume the mission in the morning if necessary.
The man had been on Raoul Island, about 1000km northeast of Auckland and renowned for volcanic eruptions and almost daily earthquakes, since October on a six-month stint of duty.
He was one of four volunteers helping three DoC staff, who monitor seismic and volcanic activity as well as conduct conservation work such as eradicating weeds to protect the more than 100 plants which are native to the Kermadecs.
They are the only people on the island, which is a tightly-controlled nature reserve.
The missing man's family had been notified, as well as the relatives of other workers on the island.
- By Matthew Backhouse of APNZ and Mathew Dearnaley of the New Zealand Herald
