"It's a great tragedy, these things can happen when you've got international tourists on your roads, but obviously it's a great tragedy and our sympathies go out to the families,'' Mr Key said on TVNZ's Breakfast show today.
Daniela Rosanna Lekhno, Roch Jauberty, and Austin Brashears were killed on Saturday when the people-mover they were in rolled, throwing several occupants from the vehicle.
Their parents are now on their way to New Zealand.
The vehicle was on of two filled with exchange students from Boston University on their way to walk the Tongariro Crossing.
A 21-year-old woman who is in a critical condition after six hours of surgery on Saturday.
Two other women, aged 20 and 21, remain in Rotorua Hospital in a stable condition.
A 21-year-old woman and a 21-year-old man were treated in Taupo Hospital and later discharged.
The group in the second vehicle were also Boston University students except for one man who is from another American university visiting a friend.
Early indications were that the vehicle drifted into gravel then overcorrected.
Students at Boston University held a candlelight vigil and remembrance on campus yesterday to pay tribute to their friends.
AA spokesman Dylan Thomsen described the triple fatality as tragic, while other road safety groups fear it might have been "avoidable''.
The New Zealand Transport Agency said since police revealed some of the victims were thrown from the vehicle, it suggests they may not have wearing their seatbelts.
Safety campaigner Clive Matthew-Wilson, thought the poor design of the road might have accounted for the smash.
"It's been known for decades that if the edge of a road drops down into gravel, then vehicles that drift over the edge of the road are likely to drop one wheel into gravel, slide and then lose control. That appears to be exactly what happened with the Turangi tragedy.''
He said similar tragedies could be avoided by extending the asphalt by 300mm beyond the edge of the verge-side white line, or by putting in rumble strips.
