Prime Minister Bill English has picked apart a news report based on leaked video evidence which suggested the Pike River coal mine was safe to re-enter.

English also rejected claims of a cover-up, saying that the video footage was not "secret" or "hidden" and parts of it had been viewed by families of victims six years ago.

Earlier today, the Government and New Zealand Police were accused by Pike River miners' families of holding back the footage, which was taken by a robot from inside the mine's drift in March 2011 - four months after a gas explosion killed 29 miners.

Speaking at his weekly press conference, English gave a detailed criticism of a Newshub report which aired last night and was based on footage leaked to the miners' families.

Source: Newshub

"It was suggested the footage showed the mine was safe to enter, that workers had been well down the drift, and that this countered the expert view that manned entry is unsafe.

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"I can understand the families being upset with this information, but it turns out the claims are incorrect."

The Mines Rescue Trust has confirmed that two staff members featured in the video were in a container at the entrance of the mine, rather than deep inside the mine where the methane levels were very high. They travelled just two metres into the drift, English said.

Police said today that families had been shown excerpts of the video footage at meetings in Greymouth in July 2011. Around 30 family members and supporters were at the meetings.

It is not known whether all of the dead miners' family members were at the meetings.

The footage is 20 to 30 hours long, and it is also not clear whether families were shown parts of the video in which the robot appears to emit smoke while inside the mine's drift.

Some, including Opposition MPs, have claimed that this proved the mine was safe to re-enter, given no explosion was caused.

This was dismissed by mining experts who said the atmosphere was inert and an explosion was highly unlikely.

Last night, police told Newshub that they did not hand over the footage to a Royal Commission of Inquiry into the mining disaster because it was assessed as having no evidential value. This added to the families' feeling of a cover-up.

Police deputy commissioner National Operations Mike Clement said today that the police had mistakenly been referring to an earlier piece of video evidence taken inside the mine in November 2010. English confirmed the March 2011 footage had been turned over to the commission of inquiry.

State-owned coal miner Solid Energy, which runs the mine, also considered the video footage when it assessed whether the mine was safe to re-enter.

"The video does not change the assessment that the mine is unsafe for re-entry," English said.

The Government has ruled out manned re-entry on health and safety grounds. Solid Energy is now looking at unmanned re-entry of the drift, possibly with the use of a drone.

English said it would be difficult to get closure for the dead miners' families.

"Anytime you meet with them you can see the grief. We will do our best to get as much information for them without taking the fairly significant risk of putting other people into an unsafe mine.

"A mine explosion is a bit of a binary kind of thing. You have one or you don't. You don't get little ones and come out with a broken arm. You either come out safely or you come out dead."

Labour and New Zealand First say they will investigate manned re-entry if they come into power in September.