‘We won’t forget this day’: Witnesses tell of the horror
It started with tourist footage showing wisps of steam gently rising from the crater.
Less than 30 minutes later, New Zealand's Whakaari volcano was spewing violent clouds of ash thousands of metres into the air.
The eruption came with little warning at 2.10pm on White Island in the Bay of Plenty off the north coast of the North Island.
Like scenes from ancient Pompeii, footage captured by tourists and shared on social media showed ash-covered survivors on a large rock, scrambling to board a rescue boat.
In other remarkable footage, a helicopter can be seen with rotor blades sagging and snapped under the weight of the dust.
A number of New Zealanders and tourists - including a number of Australians - were on or near the island when the volcano erupted.
American tourist Michael Schade said he had only just left White Island less than 30 minutes before it exploded and was "waiting for the boat to leave" when he witnessed the carnage.
"My god, White Island volcano in New Zealand erupted today for (the) first time since 2001," he said.
He said his boat rescued some of the survivors and his mother as among those tending to the injured.
"My family (on the) boat ride home tending to people our boat rescued was indescribable," he said.
"Those are some of the people put boat picked up. Praying for them and their recovery.
"(A) woman my mom (sic) tended to was in critical condition but seemed strong by the end. The helicopters on the island looked destroyed."
Mr Schade described the incident as "hard to believe" and said: "Our whole tour group were literally standing at the edge of the main crater not 30 minutes before. My thoughts with the families of those currently unaccounted for, the people recovering now, and especially the rescue workers."
In other gut-wrenching scene, New Zealand's GeoNet volcano cameras depict a group of about 19-22 people walking on the volcano's crater rim moments before the explosion.
Seconds later the camera is destroyed by the blast.
In other footage shared on social media, tourists on a boat close to the erupting volcano are ordered over loudspeaker to "go inside right now" to take cover from the looming cloud of ash.
Brazilian tourist Aline Moura, who lives in Australia, was in a boat close to the island when the volcano erupted.
"This was the end of today's trip," she posted on Instagram.
"The beginning was excellent, lots of cool pictures, amazing experience!
But nature is autonomous and man has no control over his will.
"Surely we (will) never forget that day.
"Let us pray that everyone will be fine!"
New Zealand business consultant Ange Wallace posted a selfie with the Ovation of the Sea in the background.
"I loved watching #ovationoftheseas arrive into Tauranga this morning while listening to the most beautiful version of 'Forever Young'," she said.
"So sad to hear that many of the people who were on White Island when it erupted were from this ship."
"Hearts going out to everyone affected and their families and friends".
At the request of New Zealand Police, New Zealand Red Cross established the Family Links website for people to register themselves as safe and to seek information of possible missing people.