New Zealand ? A flash flood struck a high school hiking group at a wilderness gorge in New Zealand, sweeping six teenagers and a teacher to their deaths in a tragedy that shocked the country.

Five other students were plucked to safety from the torrent Tuesday in the Mangatepopo River in the Tongariro National Park on New Zealand’s North Island.

“It is a tragedy which defies belief,” said principal Murray Burton of the Elim Christian High School in Auckland, New Zealand’s largest city.

The six students who died were all aged 16 and the teacher was 29.

Officials said there was no apparent warning to the group when the river rose to about four times its normal water level in the narrow gorge within half an hour.

The teenagers were part of a group of 40 students attending a weeklong course at the Sir Edmund Hillary Outdoor Pursuits Center in the small town of Turangi. The course involved navigating the gorge by swimming, clambering over rocks and hiking.