Search and rescue teams are out looking for a woman and four children who have been missing in Te Urewera National Park for two nights.
Police said they were alerted just before 4pm yesterday when the group were reported overdue from a walk in the forested Bay of Plenty area.
The age of the children ranges from four to nine.
They had been dropped off just after 1pm on Tuesday for a one to two-hour walk.
Search and rescue teams and a helicopter searched the Otamatuna Ridge area overnight and were continuing their efforts around the northern area near Lions Hut today.
Te Urewera Treks guide Hinewai McManus said the area around Waimata Valley where Lions Hut is located was a tricky place to go, particularly at this time of year.
She said people had to take care, particularly in winter, with only only one main road going in or out and a lot of water systems making flooding possible.
Heavy rain could make it impossible to get out at times, she said.
Ms McManus said the area did not get cellphone coverage so people were normally encouraged to take a personal locator beacon.
Mountain Safety Council chief executive Mike Daisley said it appeared the group were not prepared for an overnight stay.
"This is the third 'unexpected night out' in as many weeks, and the second involving an adult and a group of kids."
"It's a real concern that people are heading out in winter without considering the possibility that things might not go according to their plan, especially with kids involved."
"We'd urge all those going for a day walk to make themselves familiar with the outdoor safety code, and importantly leave an intentions form so you can be more easily found if the unforeseen happens."