Families of the Pike River Mine disaster will meet at the foot of the doomed mine today, on what should have been the first day of the re-entry mission.
Re-entry into the mine was postponed at short notice yesterday afternoon, after experts found "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".
But families of the 29 men who died in the mine explosion, alongside politicians - including Prime Minister Jacinda Ardern - will still gather at the entrance to the mine shaft for a planned service.
Deputy Prime Minister Winston Peters and Pike River Recovery Minister Andrew Little will also be there, as well as Green Party co-leader James Shaw and National Party Pike River spokesman Mark Mitchell.
The families will also be given more information about the delay from Pike River Recovery Agency (PRRA) bosses Dave Gawn, Anna Osborne and Dinghy Pattinson.
Proceedings begin at 11.30am with a formal address, followed by the PRRA bosses, then a moment of reflection.
Expert miners were due to enter the West Coast mine this morning in a long-awaited bid to try to recover the 29 men who were killed in the November 19, 2010, disaster.
The PRRA has been working for months to purge methane and oxygen from the mine by pumping in nitrogen before they enter it. But Wednesday's unusual oxygen reading caused safety concerns strong enough to postpone entry.
Making the shock announcement yesterday afternoon, Little said: "Yesterday [Wednesday], unexpected and unexplained readings were reported by the atmospheric monitoring systems in the Pike River mine, leading to re-entry operations being suspended."
Operations were immediately shut down, and experts will now try to locate the cause of the oxygen leak. Animals nibbling through tubes is one possible explanation.
It is not known how long the postponement will last, but PRRA bosses said they will "definitely" still go in.
"This is only a hiccup. They are working very hard to correct this," Osborne said
The Pike River families were disappointed, but said they understood that safety came first.
Families had been readying themselves for an emotional moment when the 30m-seal at the mine's entrance was to be breached.
It has been more than eight years since the heartache from the loss of 29 men's lives, outrage over attempts to permanently seal the mine - which the families successfully fought - and frustration at the lack of accountability.
They've also wanted it to be treated as a crime scene, and any clues which may lead to a future prosecution, gathered and explored.
After the methane gas explosion, fears of further explosions prevented any search-and-rescue attempts.
Toxic gas levels and safety concerns meant the first attempt back into the mine – four days after the initial explosion – came with a New Zealand Defence Force robot sent underground. It broke down just 550m in after reaching water.
Four more robots would go in, with mixed results, including video footage on November 25, 2010, from 1600m into the mine, which showed extensive damage from the second blast and ended hope of recovering the 29 trapped miners.