Volcanic ash from White Island has prompted volcanologists to raise its alert level from 1 to 3.

The minor emission of ash was "passively emitted" from a vent late on Tuesday morning, GNS Science duty volcanologist Steve Sherburn says.

GNS Science was unsure of implications for visitors to the Bay of Plenty island and would release more information later in the afternoon.

The volcanic alert level ranges from 0 to 5, with 3 indicating eruption hazards near the vent.