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.
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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.