The Pike River Recovery Agency has begun clearing out the remnants of a barrier built 30m into the mine's drift.
The work is the latest step in efforts to re-enter the mine, and paves the way to another barrier that hasn't been breached since 2011.
The 30m barrier was erected in 2016 when it looked likely the site would be sealed permanently -- before the families of the 29 miners killed in the 2010 explosion fought to stop that happening.
The Pike River Recovery Agency's chief operating officer, Dinghy Pattinson, said the work would allow workers to prepare to breach the second barrier, 170m into the drift.
"Beyond the 170 is where no one's been since 2011, where we're currently working now between the 30 and the 170 no one's been there since Solid energy sealed it in 2016 so for us it's a milestone to actually get rid of that 30m wall, get our machinery and that in beyond that point and so we can do some other jobs between the two walls."
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Mr Pattinson said there was a lot of work to do before the second wall could be breached however.
The infrastructure which has prevented water from building up in drift needs to be removed and today workers took out massive concrete panels that formed part of the wall at the 30 metre barrier.
Mr Pattinson said the whole job is expected to take at least four weeks.
"It's just slow, slow work and it's work that you have to take your time doing because you're in a confined space, you've got machinery, you've got people working around so you can't rush it, you've just got to take your time doing it."
Pike River Recovery Agency engineers work to remove the 30m barrier and dewater the infrastructure at the mine site. Photo: Pike River Recovery Agency / Supplied
He said it would be worth it when workers could breach the second barrier and he was confident they could reach it.
"I haven't seen anything to date that would be a showstopper, you know, we've still got a lot of planning and things to do yet before we breach it but there's nothing there that concerns me that we can't get through."
The only impediment to the mine workings beyond the second barrier is a rockfall more than 2km into the drift.
The agency said in a statement today the process of removing the 30m barrier, "weirs, concrete blocks, gabion baskets and grizzlies" was expected to take some weeks.
Bernie Monk, whose son Michael was killed in the explosion, said breaching the second barrier would simply mean rolling back the clock on the work done to stop the families getting in and getting answers.
"It's almost, you know you say to yourself 'what are they hiding and why have they gone to this situation to stop us from going in', when the experts that we've got on board said there was no reason why it couldn't have been done irrespective of the disaster that happened.
Bernie Monk Photo: RNZ / Conan Young
"People just put obstacles in our way."
Mr Monk said he was already thinking beyond the 170m barrier and what may be found there.
The Pike River Recovery Agency said that after work was carried out to prepare the drift up to the second barrier, any plan to proceed beyond it would require the support of WorkSafe.