WELLINGTON - New Zealand geologists confirmed Thursday that a second volcano had erupted this week?and warned further eruptions could happen at any time.

The Institute of Geological and Nuclear Science (GNS Science) issued a statement saying White Island, a marine volcano about 50 km off the east of the North Island, was erupting an "ash charged plume," making it the island's first eruption since 2001.

The ash was only rising 200 to 300 meters above the active vent, making it a "weak" eruption, but the vent had also started showing a cone.

Impact craters around the vent signaled material had been ejected in explosions, said the statement.

GNS Science warned that visitors to White Island, a popular tourist attraction, were at the highest level of risk since the end of the 2001 eruptions.

"Additional hazards to visitors to the island now include the health effects of volcanic ash and acid gas exposure, including respiratory issues, skin and eye sensitivity to acid gases. Explosive eruptions can occur at any time with little or no warning," it said.

Meanwhile, GNS Science said early testing of ash from Mount Tongariro, in the central North Island, had confirmed the eruption late Monday was steam-based and emitted little magma.

Head of Vulcanology Gill Jolly told Radio New Zealand that meant the eruption was caused by gases and heat coming from below.

GNS Science maintained Tongariro's Volcanic Alert Level at Level 2, indicating that activity is low level but renewed unrest is possible.

Tongariro is a complex of multiple volcanic cones created over 275,000 years, and its last previous eruption was in 1897.