The "symbolic" re-entry to the Pike River Mine drift is something best left to the families of the men who were killed there, Prime Minister Jacinda Ardern says.

A renewed attempt to re-enter the Pike River mine will occur tomorrow.

Pike River Recovery Agency chief executive Dave Gawn said the agency had completed preparations for re-entry, including cutting through the concrete seal and providing ventilation.

"Assuming favourable weather conditions and no other last-minute issues arising, the agency will re-enter the Pike River Mine drift tomorrow," Gawn said in a statement.

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"At the request of families, tomorrow will be low-key and private for families to witness the opening of the double airlock doors and the re-entry team stepping through."

The re-entry is a long-awaited goal for the families of the 29 men who died following the 2010 explosions in the West Coast mine.

Sonya Rockhouse, whose 21-year-old son Ben was killed, said the families had thought it would be nice if the event was for them only given how long they had been in the media spotlight, she said.

A well-publicised re-entry attempt was planned for May 3 but called off by the Pike River Recovery Agency the day before for safety reasons.

Ardern, who visited the families ahead of the May 3 attempt, said the decision was made then that any future attempt should be left to them.

"It is really a symbolic moment. Re-entry to the drift is going to take a number of weeks and months. It's a progressive piece of work as they move beyond, of course, the barrier created by the concrete which will be removed as I understand it in the coming days," she said today.

Prime Minister Jacinda Ardern says the Pike River Mine re-entry is for the families. Photo / Mark Mitchell
Prime Minister Jacinda Ardern says the Pike River Mine re-entry is for the families. Photo / Mark Mitchell

Bernie and Kath Monk, who lost their son Michael in the disaster, would be attending tomorrow, Bernie Monk told the Herald today.

He said the families had been invited to meet at 10am and they would be driven to the mine.

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"We just got a message from the agency … They are making it available for them to come up if they want to see the first wall taken out tomorrow, the 30m wall [inside the mine entrance]."

Asked if he was excited the re-entry was about to start, he said "Yeah I am. It's something that should have been done eight years ago. History will be made tomorrow."

He was confident that the problems that had prevented the attempt on May 3 had been overcome. "It wasn't a big issue; it's just something that happens in mining."

Workers were last week back cutting into the concrete seal plugging the Pike River Mine drift after the leaky tubes that delayed the long-awaited re-entry were replaced.

Families were disappointed by the delay but accepted safety must come first.

The agency had been working for months to purge methane and oxygen from the mine by pumping in nitrogen before they were to head underground.

But the day before they were due to go in, they got an "unknown reading of oxygen" from a borehole 2.3km into the mine's drift, where the roof collapsed in the 2010 explosions. The oxygen had the potential for a "spontaneous combustion event".

A leaky sampling tube was to blame for the oxygen spike and was replaced before work on cutting into the concrete seal resumed.