New Zealand's most active volcano is primed to blow again, just days after scientists thought it had calmed down enough to lower alert levels.

Unsettled activity at White Island, which has prompted authorities to raise alert levels, indicates the volcano could erupt at any moment.

Hydrothermal activity at White Island has increased and experts say there is "significant concern" the volcano could erupt with little or no warning.

Fireworks are believed to have been responsible for a large fire in the crater of Auckland's Mt Eden early this morning.

New Zealand scientists are hoping to capture new deep-sea species when they head out to one of the world's deepest undersea trenches this week.

The steam and super-heated gases which have been pouring from the side of Mt Tongariro since two surprise eruptions last year are set to be a feature for years.

Plumes of "smoke" seen rising from Mt Tongariro today are not signs of increased volcanic activity, say GNS scientists.

After Mt Tongariro spewed ash into the sky, scientists are closely watching its potentially more destructive neighbour Mt Ruapehu.

The immediate threat of eruption at Mt Tongariro has passed but there remains a chance of another sudden eruption within the next two weeks, GNS Science says.

Tamatea Intermediate School's volcano studies took on unexpected realism as Tongariro erupted in front of a fifth of the Hawkes Bay school's pupils on a trek during their end-of-year camp yesterday.

Police say they would "discourage" sightseers from travelling to Mt Tongariro following an eruption at the Te Maari crater today.

These images from the GeoNet camera at Te Maari Crater show the scene changing from 11.30am to 1.30 pm today, when an eruption occurred.

Scientists are warning there are heightened signs of volcanic activity at Mt Ruapehu and an eruption could be just weeks away.

Prime Minister John Key says he was made aware a few days ago that there was increased activity on Mt Ruapehu.

A Kiwi scientist has helped discover a monster volcano under Hong Kong - one of just 50 'supervolcanoes' worldwide on the scale found under the city.

Officials are looking at reopening tracks which have been closed since the mountain's eruption.

Tongariro erupted late on August 6, throwing out rock, ash and steam. It was the first time since 1897 that it had erupted.