Locals this week took pictures of steam pouring from White Island, also known as Whakaari.
Scientists yesterday flew over the island to look at the eruption. Experts say black ash was reaching 3km above the active vent on the southwest corner of the volcano's crater.
GNS volcanologist Brad Scott said: "This is the first ash emission from White Island since February 2001 and represents the start of a new phase of volcanic activity at White Island."