Five to six metre swells in the Western Bay of Plenty were hindering the search for a missing boat with five people aboard on Monday evening.
Two adults, two teenagers and a child set off from Maketu earlier in the day, and the boat's skipper alerted his wife by text message just before 1.30pm that they were lost at sea.
The 5.5m fibreglass recreational vessel was equipped with a marine radio and compass, but rescuers were not able to make contact with it.
Sergeant Craig Madden of Tauranga police said concern was mounting for the safety of those on board, but he said the boat's occupants had lifejackets.
The Rescue Co-ordination Centre, Coastguard, a helicopter and local fishermen were also involved in the search.