Rescuers were searching for up to eight teenage students at an outdoor program who were missing after being swept away by a raging river in New Zealand, officials said Tuesday.

At least three other students were rescued. Police Inspector Paul Jermy said weather conditions, described as "rugged," were hampering the search.

Jermy said the students were swept away by rising water levels in the Mangatepopo River in central North Island's Tongariro National Park.

The teenagers 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.

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

Inspector Steve Mastrovich said a helicopter flew over the river before dark and another with night vision capability was traveling to the area to help with the search.

Search and rescue teams were also searching the area.

Murray Burton, principal of Elim high school in Auckland, where some of the teenagers studied, said they 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," he said.

The grandfather of one Auckland student told the New Zealand Press Association news agency that he understood the students had been split into four groups and one group was missing.

"They'd been in camp for three or four days and today a river trip was supposed to have been the highlight," the agency quoted him as saying.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.