There is no intention to change the health and safety legislation at this stage.
She said the Government was committed to re-entering the mine, but it will be a decision will be ultimately up to Andrew Little as Minister for Pike River Re-entry.
Little said the agency would be in charge of all the legal obligations to do with the re-entry work.
The Government has put aside $7.6m per annum over three years for the agency's work.
Ardern said there may be evidence that the agency uncovers around safety risks.
"There may be evidence we're not aware of. If that happens we will work through that together (with the families)."
She hoped the agency's work would give "the Pike River families much overdue closure, and, if indeed it is possible, peace of mind".
Ardern said it was paramount for the Government to include the families of those who lost men to the disaster, as they had been kept at arm's length by the previous Government.
The agency will take over Pike River assets from Solid Energy by the time it enters liquidation in mid-March 2018.
The agency will maintain mine infrastructure, manage ongoing mine safety and mine safety while work on re-entry is undertaken. It will seal the mine (with a reversible seal) and rehabilitate the site once work on re-entry is complete.
The site will then return to the Department of Conservation for ongoing stewardship, including the planned Pike29 Memorial Track as part of the Paparoa National Park.
The agency's stated objectives are:
• Gather evidence to assist in ascertaining what occurred at Pike River Coal Mine
leading up to and on November 19, 2010 and subsequently, in order to assist in
preventing future mining tragedies and in promoting accountability for this mining
tragedy.
• To give victims' loved ones overdue closure and peace of mind; and
• If possible recover any human remains.
"We're now making great strides"
The announcement was warmly welcomed by Pike River families.
Bernie Monk, who lost his son Michael in the disaster, says the agency represents a huge step forward for truth and justice.
"After seven years of stalling and of being fobbed off by the last government, we're now making great strides towards re-entering the drift and recovering remains and evidence.
"This is really important to us, but it is also important to all of New Zealand, we should not be a country where a crime-scene goes unexamined for seven years."
Anna Osborne, whose husband Milton died in the mine, says the involvement of family members in the creation of the agency shows the job will be done properly.
"This is a transparent and inclusive process and we've made it clear that safety comes first. That's because we are confident that this can be done safely and have local and international experts who are just as confident.
"For years now we have been asking for our experts to be involved and for there to be an open discussion about the real nature of the risk involved."
Sonya Rockhouse lost her son Ben in the mine and says she is immensely pleased with how quickly things are going.
"We weren't expecting this to be such a top priority and to have an agency created within a month of the new Government forming is just so exciting. It really feels like we're hitting the ground running."
Little and other Government ministers attended Sunday's ceremony that marked the seventh anniversary of the disaster that took the lives of 29 men.
The former National government had rejected the families' pleas for a manned re-entry as too risky. Solid Energy had planned to fill the mine with concrete, but the families occupied the mine access road in January to prevent that happening and the plan was eventually abandoned.
At yesterday's ceremony, Little gave back to the families the keys to the gate that was erected to stop them going up the road to the mine.
