"On behalf of the Government, I want to reiterate my apology to the families, friends and loved ones of the deceased men for the role this lack of regulatory effectiveness played in the tragedy," he wrote.
He said he "deeply regretted" the loss of life and the suffering caused.
Commenting on the body recovery operation, he said a focus on exploring the drift (main tunnel) appeared a potentially realistic goal.
"If a safe, technically feasibly and financially credible plan for exploration of the drift can be developed the Government would be willing to contribute funds, provided the plan has been prepared by, or has the support of Solid Energy, and provided it satisfies the requirements of the High Hazards Unit."
Mr Key told the families he hoped the Royal Commission had provided them with answers, "at least in some small way to achieve some closure".
- The Greymouth Star