Six high school students and a teacher died after being swept away in a raging river Tuesday during an outdoor adventure course in a rugged New Zealand national park, officials said.

Five survivors were rescued after the 10 students, the teacher and a course instructor were carried away by rising waters in the Mangatepopo River in North Island's Tongariro National Park.

The survivors were in good condition and will be evacuated Wednesday, said police Inspector Dave White said.

"Conditions don't allow their recovery by helicopter at this time ... and we will be better placed to carry out recovery at first light," White said in a statement.

The teenagers from Elim Christian High School in the northern city of Auckland were part of a group of 40 students attending a weeklong education course at the Sir Edmund Hillary Outdoor Pursuits Center in the small town of Turangi.

Murray Burton, principal of Elim Christian High, said the group of 12 were on the river when they became separated from the main party.

"From what I understand they were well equipped for the journey with wet suits, life jackets and harnesses," he said. "It is a fairly standard sort of activity. I guess it was the (outdoor center's) call as to whether they should still go (out in the conditions), and I have no reason to doubt their judgment."

It was not clear whether they were in a boat or crossing the river on foot.

Inspector Steve Mastrovich said a helicopter with night vision capability swept the river after dark.

"It looks as though there has been sudden flash flooding," he told reporters.

Prime Minister Helen Clark said she was "shocked" by the deaths, which were "every family and school's worst nightmare."

But Clark, a mountaineer, said the tragedy should not stop young people undertaking supervised adventure activities.

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