Auckland, Jan 22 NZPA - Grieving families of six students and a teacher killed in a river tragedy last year have welcomed guilty pleas from the adventure school involved but say the pain is still huge.

The Sir Edmund Hillary Outdoor Pursuits Centre (OPC) announced today it was pleading guilty to two charges laid by the Department of Labour after the teacher and students were swept to their deaths when a wall of water surged down the Mangatepopo Gorge near Turangi in April last year.

The centre said the two guilty pleas related to charges of failing to take practical steps to ensure the safety of an instructor and failing to take practical steps to ensure no action of the instructor harmed the members of the group.

Two other charges were withdrawn by the Department of Labour and a date has yet to be set for the centre to be sentenced.

OPC trust board chairman Rupert Wilson said today several of its staff had stood down following the tragedy.

But he would not say how many were involved or whether they would return to work.

Mr Wilson said today the Mangatepopo Gorge would stay closed until the inquiry into the tragedy was finished.

He said the centre was still very conscious of bereaved families' grief.

"The Sir Edmund Hillary Outdoor Pursuits Centre acknowledges and truly regrets that on this occasion, it did not fully implement the standards of safety and care which OPC prides itself on," he said.

Today the chairman of the Elim Christian School Trust Board, Danie Vermuelen, said the school and the families welcomed the guilty pleas.

It said the OPC had accepted "responsibility and accountability for its actions".

"We are hopeful that it will now be possible to conclude the remainder of the police investigation and the coroner inquest much earlier than anticipated.

"This journey continues to be a most difficult one for our families. The pain is huge and the loss is felt every moment, as it does for any other families who have prematurely lost loved ones.

"Whilst we support accountability and have confidence in the legal system to follow due process, there will never be closure.

"While nothing can erase what has happened or restore our broken families, we want to ensure that as a consequence of this unfortunate process that a tragedy of this kind can be averted in the future and adventure activities of this kind made even safer," Mr Vermuelen said.

He said the school had yet to decide when students would return to the OPC but that decision would be made after consultation with the bereaved families, the wider parent community, teaching staff and students.

Those who died were teacher Anthony McClean, 29, of Howick, and students Natasha Bray, 16, of Pakuranga; Portia McPhail, 16, of Manurewa; Huan (Tom) Hsu, 16, of Farm Cove; Anthony Mulder, 16, of Howick; Floyd Fernandes, 16, of Howick, and Tara Gregory, 16, of Mt Wellington.