The government has confirmed the process to re-enter and recover the access tunnel to the Pike River Mine will begin on 3 May.
Pike River Portal and fan Photo: Supplied / Pike River Recovery Agency
Minister Responsible for Pike River Re-entry, Andrew Little, said in the past few months there had been an "incredible amount of preparation" to get ready for re-entry to the mine where 29 men were killed in 2010.
Speaking at Parliament, Mr Little told reporters he had a "high degree of confidence" workers would break through the 30 metre concrete seal.
"I've been very careful, from my point of view, about not putting undue pressure on the project to rush into it, but having been down there...we are confident that we can meet that real start date."
Mr Little said the "skilled team" would go only as far as the rockfall at the end of the drift and it was "hard to predict" how long that would take.
The tunnel ran uphill and so would be a "pretty arduous" task, Mr Little said.
"The pace at which they make progress will depend on those early days and early weeks to see what they find and how they go."
A "phenomonal amount of work" had been done in preparations and workers were now waiting on vital equipment to arrive from Australia in early April.
"I've been round the hillside and climbed up virtually vertical cliff faces - that's the terrain that they've had to work on. It has taken time, it's been done well, it's been done properly, it's been done safely."
Families of the victims previously expressed a desire to go into the tunnel themselves.
Mr Little said the government would consider whether that was viable "at some point", but the start point was getting the trained team inside.
Andrew Little speaking about the re-entry plans today. Photo: RNZ / Rebekah Parsons-King
Re-entry workers had been trained in a forensic environment, Mr Little said.
"Worksafe have been reviewing all aspects of the planning, risk assessments and supporting documentation, in order to ensure the re-entry plan is safe.
But there was still preparatory work to do, Mr Little said.
"There is still some work to do: Installing compressed air lines; awaiting the arrival of underground equipment such as loaders, roof bolting rigs, a driftrunner and a refuge chamber from Australia and breaching the concrete seal at 30 metres.
"Once the 30m seal is breached, then the re-entry and recovery operation can begin."
Work to flush explosive gases out of the 2km-long mine tunnel began in January. That meant pumping nitrogen in every day for 12 hours a day for several weeks.
Last month documents released by the Pike River families show the handling of exhibits from the mine was mismanaged, with the inquiry head at the time detective Superintendent Peter Read describing the chain of evidence as "diabolical".
The revelation casts doubt on whether a potentially crucial piece of evidence to the cause of the explosion, a switchboard door, would ever be found.
Some victims' families learned of the existence of a photograph of an electrical cabinet door that was blown to the mine surface - but no one can say where the mangled piece of metal has gone.
Mr Read said exhibits, including photos and video, arrived at the investigation base with no documentation so they had no idea when or where they had been taken.
Police, who had been training to enter the tunnel, said last September they would only do so if the mine re-entry plan was approved by both the Police Commissioner and an independent review.