A 69-year-old man and a 14-year-old boy are lost in Te Urewera National Park.
Their emergency beacon was activated just before 5 Sunday afternoon.
It's believed they're near Maungapohatu Marae, and a ground team is trekking through the surrounding area trying to find them.
Two helicopters sent in earlier turned back because of low cloud cover.
The Rescue Coordination Centre was in contact with them earlier yesterday evening.
It's not known if the ground team will be able to continue searching throughout the night.