White Island volcano: All you need to know

New Zealand's most active volcano erupted violently on Monday with at least five people killed and 10 still trapped on White Island.

Here's all you need to know about the deadly volcano eruption:

What is the island volcano?

The volcano on New Zealand's tourist White Island is the most active volcano in the country.

About 70% of the volcano is under the sea and at least 10 000 people go to see it every year.

The White Island, also known by its Maori name Whakaari, is about 50km from the east coast of North Island. 

The volcano's last fatal eruption was in 1914 when it killed 12 sulphur miners. White Island became a private scenic reserve in 1953.

What happened at the volcano?

On Monday at about 2pm local time the volcano erupted killing at least one person and leaving about two dozen still trapped on the tourist island.

GeoNet agency, which had been monitoring the rumbling volcano, raised its alert level to four out of a maximum five. The White Island is about 50km from the east coast of North Island.

The "short-lived eruption" threw an ash plume about 3 658m high, New Zealand's geoscience agency GNS Science said in a statement, adding there were no current signs of an escalation.

The eruptions also sent debris into the air. Video emerged of some visitors stuck in a crater, while rescue operations were on hold until conditions became safe.

The images showed smoke first engulfing the top of the crater and then the entire island.

Who was on the island?

Police initially said there were 100 people on or near the island, then later revised down the number to 50.

Prime Minister Jacinda Ardern said there were "a number" of tourists in the vicinity, both from New Zealand and overseas. Those injured - numbering about 20 - suffered burns.

Police said number of missing people on the island was "in double digits".

Was the eruption expected?

GeoNet warned on December 3 that "the volcano may be entering a period where eruptive activity is more likely than normal".

But the geological hazard monitoring website added "the current level of activity does not pose a direct hazard to visitors".

Several eruptions have taken place on White Island over the years. The most recent in 2016 left no one hurt.