Six students and a teacher from the co-educational Elim Christian College, in east Auckland, died yesterday after heavy rain swiftly turned the central North Island river into a torrent.
The two bodies could not be recovered overnight as they were is an inaccessible part of Tongariro National Park.
Ten students, aged 16 and 17, were part of a 40-strong group on a course with the Sir Edmund Hillary Outdoor Pursuits Centre based in Tongariro.
They were the first river fatalities at the centre for more than three decades, and police said the flood would have been difficult to foresee.
"The instructor was with them and they were just caught at the wrong place at the wrong time," Inspector Steve Mastrovich from Taumarunui police told Radio New Zealand.
The party got into difficulty in the Mangatepopo Gorge about 4pm and were swept away. The alarm was raised when they did not show up to be collected along with other students.
Five members of the group were safe, with one requiring medical treatment at Taupo Hospital after reportedly suffering head and back injuries in the raging water.
While families of the dead gathered at the centre, their sombre mood was echoed hundreds of kilometres away at Elim Christian School.
Elim principal Murray Burton was told at 5.50pm yesterday that some of the school's finest students had been lost.
Survivors would return to Auckland by bus today where they would be met by families, school staff, church and trauma counsellors.
Students were called to a special assembly to be told of the tragedy, and the school auditorium had been set aside as a counselling and grieving area.
"We will spend some time, as long as it is needed, with them," Mr Burton said.
It was not a day he was looking forward to, but he had to be strong for students, staff and families, even though he had also had his own emotional moments.
"I willingly put that aside to enter into the grief, to provide the support for those precious families who have lost their children," he said.
He struggled to describe the enormity of the tragedy.
"Any death in a school would be unacceptable...but to have six students and one teacher...and we are talking very fine young students who were lined up to be prefects next year, a teacher who is a stunning individual, a stunning man...
"Words fail...but I think on the other hand, our personal faith in God...we at least believe that he knows.
"Whatever his perspective is on the matter, we believe he had a purpose in it and we must hold onto that."
Canyoning is an adrenaline sport which involves scrambling, sliding or abseiling down riverbeds and waterfalls.
One of the risks is rapidly rising water, run-off from the hills above the gorge.
The group had wetsuits, helmets, harnesses and flotation vests, as they went through a gorge with very steep sides in parts with not many escape points.
Many school trips and tens of thousands of students have taken the trip over the 36 years the centre has been in operation.
The centre offers a five-day adventure challenge programme, which is its most popular school programme.
Around 4000 students from about 130 schools use it every year.
Centre boss Grant Davidson said the instructor with the students yesterday was an experienced physical education teacher.
"We don't put people with groups who don't know what they're doing, and she was under the supervision of a very experienced field manager who had sanctioned the trip."
"When they entered the gorge the water was at very low level and there was no prediction for heavy rain.
"Obviously if we had known or predicted about the pulse of water we would not have been there."
Mr Burton had no difficulty with the decision to go on the river in the face of severe weather predictions.
"I don't think the teacher would have consented to taking the students if he had had a doubt in his mind. Clearly it was something that happened very quickly.
"OPC have a fine record and at this stage I certainly wouldn't be judging them on that."
All tours at the centre had been suspended.
