The search for a fishing vessel carrying four people missing in waters north of Tonga is being hampered by rough seas and ash from a nearby volcanic eruption.
The New Zealand Maritime Coordination Centre, which is assisting the Tonga navy with the search, says the beacon was activated on Tuesday about 37 kilometres north of Nuku'alofa.
A spokesperson says since then, the signal has moved to be about seven kilometres from the shore, but numerous attempts by the navy to find the missing boat have been unsuccessful.
He says a P3 Orion will undertake an aerial search when the conditions improve.
He says it is not clear whether the vessel has come into problems or the beacon has fallen overboard, as while the boat has cellphones and radio, nothing has been heard from those on board.
The vessel is due back in port this afternoon.