A re-entry attempt to the Pike River mine could resume within weeks, or less, the Pike River Recovery Agency boss says.
A team had planned to begin the re-entry today to the mine near Greymouth in which 29 men died in 2010.
Families of the Pike River mine victims are being promised a comprehensive briefing today, after a change in atmospheric conditions in the mine yesterday forced a delay.
Despite the setback about 230 people - including the prime minister and those representing 14 of the affected families - are expected to gather at the mine entrance just before midday.
Pike River Recovery Agency chief executive Dave Gawn told Morning Report they were taking health and safety-first approach, as originally agreed on.
"The reality is that as we were going through the set up and the breaching of the 30-metre seal, or the first parts of it, some unexpected readings of oxygen presenting at one of the boreholes caused us to pause, because we need to actually understand what's going on."
The oxygen readings created potential for a "spontaneous combustion", he said.
"We really need to understand what's going on, understand how the mine responds to what our actions are, and take it from there to ensure we've got the safest plan possible for re-entry."
More testing is underway to understand what the cause and effect of that reading will mean, but Mr Gawn said he does not expect it to take long.
"It's not going to be months, provided we can get a really clear understanding of what's happening, so [it could be] within the next weeks. It could be that long, but it may be a lot quicker."
One theory is that there is a split in the tube bundle system or pipe being used to test the atmosphere in the mine. A split would draw oxygen from outside and suck it down into the main entry tunnel.
If there is a split, there remains the question of how it got there with one possibility being a wild animal may have chewed a hole somewhere along the 4km-long length of tubing.
A wild herd of goats is known to be loose in the area but it could also have been rats or possums.
A new pipe is being laid to test the mine's atmosphere and it's hoped this will show whether there is an issue with the equipment or if the oxygen is getting in somewhere else.
Further risks down the line were also possible but the team was prepared to deal with those as they came, Mr Gawn said.
"I think we've got a good team and a good plan, but risk is a dynamic process, it's not something set in stone from the outset. These issues will come up from time to time, I have no doubt about that, but we need to address each one of those in the safest manner possible."
The minister responsible for Pike River re-entry, Andrew Little, told Morning Report he backed the agency on its decision to delay re-entry.
Mr Little said early indications from additional monitoring equipment, put in place to see whether or not the original readings were accurate, were showing better readings.
"That's what the very early indications are but there's nothing conclusive about that because it's too early and you need several days of data to draw any conclusion about that.
"What that tends to point to is that there is an equipment issue as opposed to an unexplained issue about the strata or any atmospheric issue."
However, he said that operations would only resume once the team had a high degree of certainty about the safety and understanding of the readings.
"We prepared for that originally, that once we get something like that that's unexplained you stop what you doing and you work out what's going on."
In response to reports that Deputy Prime Minister Winston Peters had written a formal request to be a part of the re-entry team, Mr Gawn said he had spoken to Mr Peters and appreciated his desire but turned him down.
"The reality is the whole principle of the recovery and what we're doing is that only the staff essential for the task underground will go into that mine ... and as such I have thanked him for his offer and denied him the opportunity to go into the mine."
Mr Little also backed the agency on that call. He said while he understood Mr Peters' commitment to the families, the agency had statutory obligations and liability for making such decisions.
Pike River Recovery Agency has also posted a video explaining in depth what happened to cause the delay.
Sonya Rockhouse, who lost her son Ben in the mine disaster, told Morning Report that while the delay came as a shock at first, the families were staying positive.
"We know it's going to happen and we're reasonably confident it's going to happen within the next few weeks.
"We've waited eight and a half years so another few weeks is not going to make a whole lot of difference."
Ms Rockhouse said the families understood that safety was always the highest priority and they agreed with that.
"We want them to be sure, it gives us confidence ... that they'll do the right thing all the way through. We don't want anybody hurt or killed in the pursuit of doing this.
"We fully support the agency 100 percent, they did the right thing."
She said the families were still looking forward to the plan today.
"As for today not a lot has changed, everything will continue as per the plan, the pulling of the plug was really a symbolic thing today, we will be able to see where they have drilled around."