Six teenagers and a teacher _ killed in a river gorge in New Zealand when floodwaters suddenly surged down on them _ had little chance of escape, their principal said Wednesday.

New Zealanders were deeply shocked by Tuesday's incident, which devastated a high school expedition that was supposed to build team spirit and environmental awareness.

Six 16-year-old students from Elim Christian High School and their 29-year-old teacher were killed when they were overwhelmed by floodwaters that streamed down the Mangatepopo River after a violent rainstorm.

"It is a tragedy which defies belief," school Principal Murray Burton told reporters. Students clutched each other in tears as Burton read a list of those who died during a special assembly Wednesday at the school in Auckland, New Zealand's largest city.

Prime Minister Helen Clark expressed "profound sympathy and shock" and introduced a condolence motion in Parliament.

Five other students were plucked to safety from the torrent in Tongariro National Park on New Zealand's North Island. One of the survivors said he had been able to clutch a log when the waters surged, Burton said.

Officials said there was no apparent warning to the group before the river quickly rose in the narrow gorge.

"We understand that there was a flash flood which took the river probably triple, quadruple in height and equally in such a short time later, dissipated," Burton said Wednesday.

He said officials told him the victims _ three boys and three girls plus their male teacher _ had no escape route from the surging waters because of the canyon's high walls.

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 in an activity known as canyoning.

Andy Bray, whose daughter Natasha was one of those killed, told reporters it was "one of those freak moments when a lot of water poured down, one of those once-in-a-million-years kind of things."

Those swept away were in a group of 12 that had separated from the main party. District Police Inspector Dave White said the students were doing a team-building exercise traversing the river when they were overcome.

New Zealand's spectacular and rugged wilderness is world famous, and many of the country's inhabitants pride themselves on their close connection to it. Mountaineering, hiking and sailing are common pursuits among the nation's 4.2 million people.

Grant Davidson, chief executive of the center that organized the trip, said the conditions appeared safe and there was no warning of the heavy rain that quickly developed in the area.

"I am comfortable this was a normal activity we had with this age group in these sort of conditions," he told reporters. "Obviously if we had known or predicted about the pulse of water we would not have been there."

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