Labour Minister Simon Bridges says there is only a slim chance of recovering the Pike River miners under re-entry plans announced on Tuesday.
The Government has approved conditional funding for a staged plan to re-enter the underground West Coast coal mine, where 29 men died in explosions in November 2010.
The plan will cost an estimated $7.2 million and is conditional on the re-entry being safe, technically feasible and financially credible.
Work stabilising the mine's atmosphere will begin in October and it's estimated it will be safe for Mines Rescue Service personnel to enter by March next year. They won't go beyond the rockfall, behind which most of the men were thought to be.
Mr Bridges, who is also the Energy and Resources Minister, believes there's only a slim chance of finding their remains in this stage of the recovery.
But the MP for the West Coast, Labour's Damien O'Connor, says Mr Bridges is not in a position to make that call. He says he trusts local knowledge over that of the minister.
The plan has been drawn up by the mine's new owners, Solid Energy, and approved by the High Hazards Unit, which is in charge of mine safety.
Mr Bridges says it is a highly complex and technical operation, with a risk assessment to be undertaken at each stage.
He says ensuring the safety of workers is an absolute bottom line for the Government and Solid Energy.
Solid Energy chairman Mark Ford says the re-entry is a complex initiative that will require constant and formal monitoring, and every step will have an uncertain outcome.
He says each stage of the operation will have to be approved by the company's board.
Plan has head inspector's confidence
The news was delivered in person to the families of the victims by chief mines inspector Tony Forster at a meeting in Greymouth on Tuesday.
Mr Forster says the method for re-entry has been successfully used in other situations. He says while such an activity is never risk free, he is confident in the plan.
"There's probably little components that might not have been done exactly before but most of these types of jobs have been done somewhere before. Every job is unique and its the collection of the parts that make this a unique operation but we're not experimenting with unknown technology."
Mr Forster says most of the work will be able to be done remotely from outside the mine. He says he will not hesitate to pull the plug if needed.
Re-entry starts with the sealing of the main ventilation shaft, followed by the sealing of the main entry tunnel just over 2km inside the entrance, close to the rockfall.
Nitrogen will then be injected to create a buffer between the methane in the mine and the fresh air that will then be pumped into the entry tunnel.
Mr Forster says it's only at this point that a recovery team will be allowed to enter the mine.
"When people actually go into the mine, when people are at risk, that will be in the safest circumstances because it will be in a fresh air environment."
Re-entry is dependent on the weather allowing helicopters to operate, as well as the atmosphere in the mine remaining stable.
Outside the meeting a spokesperson for some of the families, Bernie Monk, said it was emotional to finally hear that an attempt would be made to search for the men's remains.
Struggling to hold back tears, Mr Monk, who lost his son Michael in the 2010 disaster, said it had taken a long time to get to this point.
He thanked those who helped the families draw up a re-entry plan almost a year ago showing it would be possible to get back into the mine.
Damien O'Connor says while it is great news that the re-entry will be funded, it is frustrating that it has taken so long.
Mr O'Connor says the families have been tormented by the knowledge a recovery mission was possible but for so long there has been a failure to make a decision.
"I think the families have been frustrated. They have spoken to a large number of technical experts; they've had advice from across the world. It's reinforced what they have always believed; this is possible to do safely."
The Green Party says re-entering the mine will provide some closure for the families of the men who died in the explosions.
West Coast-based Green MP Kevin Hague says it is hard to know whether there will be any bodies in the part of the mine the rescue teams can access.
"If there are, that will tell us something about what occurred on the mine that day and of course that's one of the reasons why it's critical for us to be able to get into the mine."
The first stage of the plan involves workers plugging the top of the mine's ventilation shaft to ensure full control of the atmosphere inside.
New boreholes will be drilled into the top of the main tunnel and a camera used to check inside.
Expanding foam will then be pumped in through a borehole to form a plug about 2.3 km into the mine, close to the rockfall.
Inert nitrogen will be pumped into the tunnel area between the foam plug and the rockfall to displace methane, and the tunnel from the main portal to the plug will be ventilated with fresh air.
Once the tunnel is safe and fully ventilated with clear air, trained mines rescue personnel will enter the tunnel.
The scope of the operation does not include moving beyond the rockfall, where most of the men's remains are thought to be, due to the unstable atmosphere.