The effort to recover the Pike River mine drift begins in earnest on Wednesday, after an emotional day for families.
A symbolic re-entry took place at the mine's portal on Tuesday, bringing a sense of joy to those who lost loved ones in the blast.
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Recovery Agency head Dave Gawn told Newshub it's hoped they will reach the previously unseen final 400 metres within four months.
"We would like to be beyond an area called pit bottom and stone and certainly considering that last phase of the operation in August/September."
But there's going to be constant worries before they get there.
"We do know that we will have severe challenges in terms of both managing the atmosphere, but also managing the integrity of the roof, because this is in the area of the Hawera fault line," Gawn said.
Whatever happens, Gawn said the agency will be ensuring the safety of the people going into the mine.
"We need to work through with Worksafe to make sure that they are comfortable with our intent in relation to the concept and plan that we currently have."
The next six to eight weeks will be spent creating a new seal further down as well as removing infrastructure.
Families say the re-opening is the first step toward justice and cheered as the door to the mine drift was opened.
Spokesperson Sonya Rockhouse told The AM Show on Tuesday the mine's reopening was expected to be a big moment.
"Pulling that plug out is like pulling the cork out of a bottle and releasing whatever... and it's just the beginning of the end of a journey for us."
Twenty-nine men, ranging in age from 17 to 62, were killed after several explosions in the mine in November 2010.
It was New Zealand's worst mining disaster since 1914.