WELLINGTON (AFP) — Students at a New Zealand high school were in shock Wednesday after six fellow pupils and a teacher were killed in a flash flood during an adventure course, officials said.

Police recovered the last two bodies early Wednesday, a day after a group of 10 students, a teacher and a course instructor were swept down the Mangatepopo River, near Turangi in the centre of New Zealand’s North Island.

New Zealand Prime Minister Helen Clark called the tragedy “the worst nightmare” for the school and affected families, as questions were raised about why the trip went ahead despite a heavy rain warning from meteorologists.

Both the coroner’s office and the organisation running the course, the Sir Edmund Hillary Outdoor Pursuits Centre, have pledged to investigate the deaths of 29-year-old teacher Anthony McClean and six 16-year-old students.

“My thoughts are with the families, the whole school community, and the outdoor pursuits centre at this sad time,” Clark said.

One of the five survivors of Tuesday’s flash flood was taken to hospital for treatment, but the others were not badly hurt.

The group from Auckland’s Elim Christian College was caught in a flash flood as they climbed out of a remote and narrow river gorge near the Tongariro National Park, as rain storms lashed the northern half of the North Island.

“We got this incredible surge of water which was unpredicted,” the head of the outdoor pursuits centre, Grant Davidson, told Radio New Zealand, noting the river’s volume had increased by 36 times in the space of 30 minutes.

But Meteorological Service forecasting manager Peter Kreft said the flash flood was in line with a severe weather warning it had issued earlier Tuesday along with a separate rain and storm forecast for the Tongariro region.

“I think the warning that was issued did a very good job of warning about the risk of very high hourly rainfalls over quite a large part of the North Island,” Kreft told Radio New Zealand.

Students at the school wept and hugged each other as they learned about the disaster on Wednesday, and principal Murray Burton said the impact of the tragedy would be “huge and far-reaching”.

Burton said he had no criticism for the adventure centre for taking the students to the river despite the bad weather forecasts.

Police Inspector Steve Mastrovich said the river gorge was narrow and there would be few places where people could get out of harm’s way in the event of a flood.