The Construction, Forestry, Mining and Energy Union is concerned the reclaiming operation being undertaken by receiver PricewaterhouseCoopers is more directed at reopening the mine for operational use rather than finding the missing bodies of the trapped miners, two of which were Australian.

"While there are media reports that preparations are being made to re-enter the mine and reclaim it for sale by the current receivers, the families have received no guarantee that recovering the bodies of their loved ones is the priority," the union said.

Key said the government only had limited input into the sale process, which is being conducted by the receivers, and the government wanted to ensure the mine was safe before re-entry.

“Now, it's not quite as straight forward as that as it might require a transfer of license and under the Crown Minerals Act that may give the Crown some ability to alter that or have some conditions on that," Key is quoted as saying in BusinessDay.

"We cannot afford to risk any more people having lost 29 brave men down there and we have to have a high degree of [comfort] the plan of recovery would actually work.

"At this point I haven't been presented with a case to do that."

Key iterated the NZ government wanted the mine entered and the bodies recovered only when it was safe to do so.