Pike River family members have made an emotional pilgrimage to the entrance of the West Coast mine where 29 men died more than eight years ago.
Expert miners were due to enter the coal mine this morning in a long-awaited bid to try to recover the men killed during the November 19, 2010 disaster.
But earlier on Wednesday, the Pike River Recovery Agency (PRRA) got an "unknown reading of oxygen" from a borehole 2.3km into the mine's drift, where the roof collapsed in the 2010 explosions.
The oxygen had the potential for a "spontaneous combustion event".
The PRRA then took the decision to delay the re-entry on safety grounds.
Today's ceremonial event is still going ahead, with families travelling up to the mine portal.
PRRA senior project manager Lloyd Steward said today is all about the Pike River families,
and encouraged them to speak freely and any ask questions of PRRA staff.
"We are here to serve you," he said.
PRRA boss Dave Gawn said the reason the agency is here is for the 29 men who are "still on the inside of the tag board" and to give voice to them.
Gawn said that while they had wanted to break the concrete seal and for an expert team of three miners to walk into the mine this morning, work has begun on breaching the seal this week.
Sonya Rockhouse, whose son Ben died in the disaster, said it was difficult to comprehend that, after so many years, they are finally re-entering the drift.
She has been hardly been able to sleep over the last few weeks, with the enormity of today finally hitting.
"We've got so close so many times."
She thanked the late life-long unionist Helen Kelly, who contacted her shortly after Pike explosion, for her help in appealing the decision to drop charges against former mine boss Peter Whittall.
Rockhouse described Kelly as an incredible woman who was incensed at the way Pike River families were treated in the wake of the disaster.
She also paid tribute to "my wee mate Anna" - Anna Osborne, chairwoman for the Pike River Family Reference Group.
Osborne's husband Milton died in the tragedy.
The two women have been central in battling authorities for years to get men back into the mine's drift.
"She is more like a sister to me, and I couldn't think of a better person to have travelled on this road to hell with," Rockhouse said.
She also thanked Winston Peters for being the first politician to listen to the families.
"This is a hugely momentous day for us Pike River families and all of New Zealand. This is what happens when you stand up for what you believe in," Rockhouse said.
Her youngster son Ben, 21, is still in the mine.
She promised him every day that she would come for him and from today she is starting to fulfill her promise.
Osborne said the tragedy was totally avoidable, with the inactions of Pike River management and other agencies robbing families of their loved ones.
It was not just about the Pike 29, she said, but about changing the working culture in New Zealand.
The chance to explore the crime scene and look for any evidence that could lead to a future prosecution was a huge part of the re-entry, Osborne said.
"May the Pike 29 never be forgotten."
The families presented Prime Minister Jacinda Ardern, as a token of their "love and appreciation", a wooden box which represents the mine where their men still lay.
PRRA chief operating officer Dinghy Pattinson said one of the founding principles of the agency was that they would never compromise safety.
And he would not apologise for making the decision yesterday to delay the re-entry.
Pattinson explained how they are still pumping nitrogen into the mine to keep it safe.
They need to turn the nitrogen off and drop the pressure behind the concrete seal before they start chipping the seal off again.
But they won't do that until they discover the cause of the unexplained oxygen.
"We're not going to put a bandaid on and carry on," he said.
Pattinson wouldn't put a date on when they will resume re-entry work, saying to do so would only add extra pressure and increase safety risks.
Pike River Recovery Minister Andrew Little said that despite yesterday's delay, the project is underway.
The agency is committed to safety and transparency, he said.
He paid tribute to the tenacious work of Rockhouse, Osborne and Bernie Monk – whose son Michael died in the mine – in getting back into the mine.
"This project is about an act of justice," said Little, hoping to call into account the corporate and regulatory failures of eight-and-a-half years ago.
Many mines around the world has the patron saint of mining and tunnelling, St Barbara, and today Little gifted an icon to be placed at the Pike River Mine entrance.
Ardern sat beside Osborne and Rockhouse during the service.
It was Ardern's first trip to the mine site, and said today the focus was entirely on the families.
"They've been waiting a very long time to get to this point where the active re-entry has begun, is underway, and they've been fighting for that for a really long time. So for me, just seeing the huge amount of emotion around that for them is acknowledgement of the work they've put in and the sense of justice they feel now for that finally happening."
Ross Harvey, whose 28-year-old son Riki Keane died in the tragedy, made the trip to the mine site from his home in Nelson.
He makes the pilgrimage every year to the site of his mining contractor son's death, and always finds it tough and emotional.
"We come down every anniversary [and] it's always hard, but now we see progress which is good," Harvey said.
"Today's been quite difficult, the whole week leading up to it, and then the news about they're not going to pull the seal out today, it's all very emotional."
Harvey supported the cautious approach and to put the safety of the re-entry team first.
"That's definitely what the families want," he said.