691 islanders were evacuated over the weekend after a volcanic eruption began on Friday and progressively intensified.
The Rabaul Volcanological Observatory's Steve Saunders said the surprise eruption on Kadovar had covered the island in ash but no lava had yet reached the surface.
Mr Saunders said it would either peter out or develop into a full blown eruption where magma and explosive gases escaped.
He said with the islanders successfully evacuated, the main concern now was whether a tsunami would be triggered and aviation disrupted.
