In a surprise move, police say they will drill 10 more boreholes at Pike River Mine as part of their criminal investigation into the tragedy.
Twenty-nine miners lost their lives at the West Coast mine in November 2010.
In the past year, the remains of up to eight miners have been seen inside the mine.
Detective Superintendent Peter Read said the drilling came after consultation with an expert mine panel as part of the ongoing investigation. It said further drilling was "imperative" to ensure investigators had all necessary information as they seek to reach a "definitive conclusion" as to what caused the first explosion.
Police had previously said they would not do more drilling.
"The families of the 29 men lost at the mine have been waiting a long time for answers, and I’m very aware that in some respects this additional drilling operation could be seen as prolonging that wait," Read said.
"However, I hope the decision also provides some reassurance to the families that police remain absolutely committed to finding out as much as humanly possible about what led to the first explosion at the mine."
Anna Osborne, who lost her husband in the explosion, welcomed the news.
"This is further confirmation of just how far the investigation into our men’s deaths has come," she said.
"Seven years ago we were being told that all that could be done had been done and that we should 'walk away'. We didn’t. We fought for the reentry of the mine’s drift and for the first borehole project and now we are getting closer to justice."
Earlier this year is was announced the Pike River Recovery Agency would be disestablished and the mine managed by the Department of Conservation as part of the Paparoa National Park.