American student Evan White who saw the aftermath of the fatal van crash says he will never forget the horror.

Three Boston University students, Daniela Rosanna Lekhno, 20, Roch Jauberty and Austin Brashears, both 21, were killed on Saturday when the van they were in crashed near Turangi on the way to the Tongariro Crossing.

Another student, Meg Theriault, suffered a serious head injury, a broken right arm and grazes in the crash and remains in intensive care at Waikato Hospital.

Two others, Kathryn Moldawer, 21, and Alys McAlpine, 20, were in a stable condition in Rotorua Hospital while two more students were treated at Taupo Hospital and discharged following the single-vehicle crash.

Evan White, who was travelling in another of the students' three vans, told the Boston University news website he first realised there had been a crash when the driver of his van looked in the rear view mirror and pulled over.

"We saw people lying in the road and saw wounded people and just felt kind of helpless," he said.

"Our first impulse was to do whatever we could, but everyone had a sense of helplessness. I helped people away from the van. Others ran to a house to get help."

Mr White said after returning to Auckland on Sunday night, the group dragged their mattresses to the common room of their hostel and slept there together.

"It hurts a lot," he said.

"We are just talking about it and trying to be very open. Hopefully everyone at BU (Boston University) can come to terms with it too, like we're trying to do here."

Another student who was travelling in Mr White's van, Dustin Holstein, would not comment on the cause of the crash, but said the road was well-maintained.

"Right now we are just trying to get through this. The best way to do that is to hold each other up and give each other the support we need," he said.

The serious crash unit is expected to complete its investigation later this week, before a decision is made on whether to lay charges.