WHAKATANE, New Zealand (CBS SF/AP) — A dream vacation took a terrifying turn for a Bay Area family Monday as they watched in horror as a volcano on New Zealand’s White Island erupted as they waited to depart its shores.

It had been a day of exploring a natural wonder for San Franciscan Michael Schade and his family. And then came the large rumble and a massive cloud of ash and steam.

“My family and I had gotten off it (the volcano) 20 minutes before, were waiting at our boat about to leave when we saw it,” he posted on Twitter. “Boat ride home tending to people our boat rescued was indescribable.”

Video Schade posted showed a landscape covered with ash and a cloud of steam pouring out of the volcano. In the distance was the charred remains of a helicopter.

“This is so hard to believe,” he posted. “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.”

Schade’s mother helped to tend to the injured — many who were severely burned.

“Those are some of the people put boat picked up,” he posted. “Praying for them and their recovery. Woman my mom tended to was in critical condition but seemed strong by the end.”

Michael Schade, Twitter photo

New Zealand officials said the blast of ash and super-heated steam killed at least five people with perhaps two dozen others missing and presumed dead. Schade and his family were among the 18 who were rescued.

Police said that the site was still too dangerous hours later for rescuers to search for the missing but that aircraft had seen no signs of life.

“Based on the information we have, we do not believe there are any survivors on the island,” police said in a statement.

Michael Schade, Twitter photo

The terrifying disaster immediately raised questions of why people were allowed to visit the island some 30 miles off mainland New Zealand after scientists had noted an uptick in volcanic activity in recent weeks. White Island is the tip of an undersea volcano.

Deputy Police Commissioner John Tims said the number of missing was in the double digits but he couldn’t confirm an exact number. Fewer than 50 people were on the island when the volcano erupted, and 23 had been taken off, including the five dead, he said. Tims said there had been no contact with any of the missing.

Most of the 18 who survived were injured, he said.

He said New Zealanders and foreign tourists were among the dead, missing or injured. Some of the visitors were passengers from the Royal Caribbean cruise ship Ovation of the Seas.

The ship had left Sydney last week and had been scheduled to sail to the New Zealand capital of Wellington on Monday night, but Royal Caribbean said it would instead remain in port on neighboring North Island until more was learned about the situation.

© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.