Breaking through the 30m seal in the Pike River mine drift on May 3 will really herald the beginning of re-entry, Pike River Re-entry Minister Andrew Little says.

Little announced today that May 3 would be the day re-entry would begin.

After a bit of delay the day, which the loved ones of the 29 men who perished at the mine in 2010 have been waiting so long for, will be marked with an event on the West Coast attended by Little, Prime Minister Jacinda Ardern and Deputy Prime Minister Winston Peters.

When Little announced the plan to re-enter the mine in November last year, he hoped the work to breach the 30m seal inside the drift would begin in February.

Advertisement

He told a parliamentary committee earlier last year that it was possible re-entry could be started by Christmas 2018 but later pulled back from that date as the difficulty of the task became apparent.

Little said today there had already been a huge amount of work already done to prepare for re-entry.

"This has included preparing bridges for heavy loads, installing a nitrogen plant, upgrading the power supply, laying many kilometres of piping for the nitrogen, drilling more boreholes, installing monitoring equipment, and purging and ventilating the drift."

Little said he was at the mine a couple of weeks ago to see what progress had been made.

"The science and engineering that goes into this project, it's pretty impressive."

And there was still more to do, including awaiting equipment from Australia.

"Once the 30-metre seal is breached, then the re-entry and recovery operation can begin. All things going to the current plan, the [Pike River Recovery] Agency expects we will be at this point by May 3rd."

Little said only a skilled team would be going into the mine

"Safety is a non-negotiable bottom line for the whole project and everyone involved, including the families.

"The re-entry will only take place if all the necessary pre-conditions have been met."

Worksafe had been reviewing all aspects of the planning, risk assessments and supporting documentation to ensure the re-entry plan was safe, he said.

It is hoped that work in the drift will enable the agency and police to investigate what caused the explosion that killed 29 men on November 19, 2010.

Little said police had been training the team to be "forensically aware" when they were inside.

"And when they come across anything that looks like it's relevant to victim identification or anything else that might be relevant then the police themselves will make a decision on who they send in or whether they send anyone in."

Little said how long it took to get into the mine depended on the progress the team made in the early weeks.

"You've got to remember that drift, that tunnel, runs uphill so it will be a pretty arduous task. You're looking at 40 metres by 40 metres at a time."

There were no plans to go as far as the rockfall. The plan was only to recover the drift as far as the pit bottom in stone.

"It will be up to them, once they get in there, to work out the pace that they can do so safely," Little said.