UPDATED 7.59pm The government has ruled out a re-entry of the Pike River mine.

It told families of the 29 men killed in the 2010 explosion that it will continue to work to seal the mine despite a plea from them to reconsider the decision to do so.

LISTEN ABOVE: Environment Minister Nick Smith speaks with Mike Hosking

The families believe it is safe to enter part of the tunnel into the mine where there may be clues to what happened.

The bodies of the men have never been recovered and the mine is in the process of being decommissioned.

Environment Minister Nick Smith said there was no new information for state- owned coal miner Solid Energy to change its 2014 view that a safe re-entry was not possible.

"I remain doubtful of claims that the mine can be safely re-entered. The mine is full of methane and is likely to have residual heat sources capable of triggering an explosion if there was a source of oxygen. There is the added risk of rockfalls," he said.

"I do appreciate the huge loss families have faced with the loss of loved ones at Pike, and the added pain of not being able to recover their men. However, you cannot justify putting further lives at risk."

Dr Smith said the single exit design of the mine was a fundamental safety flaw and the government supported the decision that re-entry was not practically possible.

Solid Energy is working to replace a temporary seal with a permanent seal about 30m into the mine's drift and Dr Smith said there was about a week's work needed to complete the first phase of the work.

It deferred work on the project for a week in the lead up to last Saturday's sixth anniversary of the disaster.

With the mine in the process of being sealed, Green MP Denise Roche wants to know why the families of the victims are being told the plug is temporary.

"When it involves a 20 metre wall and requires 100 truck loads of concrete."

Dr Smith said there's been extensive consultation with the Pike families about the design of the seal over the last 12 months.

"And changes made to it as a consequence of family representations.

Labour MP Damien O'Connor is accusing Dr Smith of ignoring independent advice that says the mine can be entered.

"And why is he trying to hide behind the veil of Solid Energy, a failed company."

But Dr Smith is holding firm that re-entry is simply not safe.

"After the loss of life at Pike, why would we now want to be cavalier about safety."

This concrete seal 30m down the drift was largely installed last week with about a week's work required to complete it.

The area the mine is in is being returned to the Department of Conservation for inclusion in the Paparoa National Park and a memorial 45km Great Walk is being created.