Footage from a robot inside Pike River mine that has been leaked to media will be considered as part of an investigation into the potential for an unmanned entry, the Government says.
Labour and New Zealand First have both questioned why the footage was "hidden", with Labour leader Andrew Little calling on the Government to immediately release all Pike footage and images.
New Zealand First leader Winston Peters said authorities' treatment of the footage showed a "huge cover-up".
"All along the police and government have maintained it was not safe for anyone to enter the tunnel. This evidence proves otherwise," Peters said.
The footage was taken from a robot that entered the mine's access tunnel in March 2011, three months after the final explosion. It has been leaked and was published by Newshub tonight.
It shows two workers in the mine drift with breathing gear. The robot gets more than 1500 metres down the drift before its way is blocked. At one point it apparently gives off smoke or steam.
Police controlled the mine at the time the video was taken, and told Newshub the footage was not supplied to families of victims or the Royal Commission because it was assessed as having no evidential value.
That has angered Dean Dunbar, whose 17-year-old son Joseph was killed in the mine, who believes the video shows the mine can be re-entered.
The mine has not been operating since a gas explosion in 2010 killed 29 workers, whose remains have never been removed because of concerns about high methane levels.
After meeting the families for the first time in February, Prime Minister Bill English asked the state-owned mining company to leave the West Coast mine unsealed and to investigate the use of drones or robots to re-enter the mine.
Terms of reference have now been drafted for unmanned entry after talks between the families, Solid Energy, and the Government, although the family last week rejected the terms because they excluded several of their key requests.
Acting Conservation Minister for Pike River Issues Nick Smith said in a statement that nobody from the Government had viewed the leaked footage, but had been advised it was used by Solid Energy as part of its investigation into whether the mine was safe to re-enter.
"The fact remains that is unsafe to do so. As we have repeatedly stated, gas levels beyond the seal are consistently around 100 per cent methane, making a manned re-entry unsafe," Smith said.
"The Government has however agreed to work with Solid Energy and the families to investigate the potential for an unmanned entry. This footage is being reconsidered as part of that investigation though that work is ongoing."
Labour and New Zealand First have committed to re-entering the mine if possible.
Reacting to the leaked footage tonight, Labour MP and West Coast Tasman MP Damien O'Connor wrote on Twitter: "Bloody lying mongrels...contempt for every West Coast miner who relies on authority".
Little said the footage published tonight casts doubt over the government's reasons for blocking a manned re-entry of the drift.
"The robot footage shows the drift is in good shape, with even the pipes largely undamaged by the explosions. There's nothing in the footage to support National's claim the drift could collapse."