"But it will also be a chance to once again see the beauty of those balloons rising above your landscape.
"I know you will all have your own way of dealing with what has happened, and only you will know when it's time to move forward.
"But what I want you to know is you have the support of all New Zealanders as you deal with this tragedy.''
Mr Key said today's service was an opportunity to pay tribute to loved ones who lost their lives.
"In part today is also an opportunity for me and you here to begin to look forward, together, and to the future.''
Mr Key said many gathered had a desire to find out what went wrong.
"As a Government, we owe it to you to find those answers. I can assure you we will do just that.''
The tragedy had touched the local community and the whole country, he said.
"That day, something went wrong, terribly wrong. There is no fairness in what happened _ a morning which started so happily and peacefully ended in terrible sadness.
"I know that sense of unfairness will be felt most strongly amongst the families of those who died in the accident.''
Mr Key said the passage of time would heal, but it would not be easy.
Carterton Mayor Ron Mark opened his address with a solemn recitation of the names and ages of the victims.
He said there would be some shyness in the community about embracing this week's Balloons Over Wairarapa festival, with some feeling perhaps it should be deferred for a year or two.
"If you are of that mind you need to know that I haven't had one family tell me that they don't want that event to go ahead.
"I have instead had many families tell me that they want to fly themselves, as a tribute to their loved ones.''
Mr Mark paid tribute to the locals and emergency services' workers who helped out in the aftermath of the accident.
"This horrific tragedy would test them to their core,'' he said.
Governor-General Lieutenant General Sir Jerry Mateparae said memories of the event would linger but the service today would act as part of the healing process.
"As we gather today to reflect on this tragedy, I urge everyone to come together, to support each other and to draw on this community's strength and resilience as you move forward.''
Those killed in the crash were pilot Lance Hopping, 53, of Masterton; husband and wife Howard, 71, and Diana Cox, 63, of Wellington; husband and wife Desmond, 70, and Ann Dean, 65, of Masterton; cousins Valerie Bennett, 70, of Masterton and Denise Dellabarca, 58, of Paraparaumu; partners Stephen Hopkirk, 50, and Belinda Harter, 49, of Lower Hutt; and Johannes Jordann, known as Chrisjan, 21, of Wellington and girlfriend Alexis Still, 19, also of Wellington.
