Twenty-nine men died at the West Coast mine in November 2010 after a series of explosions. Two workers managed to get themselves out to safety.
The mine had been sealed ever since and a re-entry attempt had been planned for Friday.
However, there were unpredicted and unexplained elevated levels of oxygen at the rockfall area 2300m down the drift, and Little said this afternoon that the operation had been temporarily suspended.
Prime Minister Jacinda Ardern, Deputy Prime Minister Winston Peters, Green Party co-leader James Shaw and National Party Pike River spokesman Mark Mitchell had been scheduled to attend.
Little said there would still be an event on Friday for the Pike River families.
Anna Osborne, from the Pike River Families Reference Group, had told him that she was disappointed but understood that the primary concern was safety, the minister said.
"Yesterday unexpected and unexplained readings were reported by the atmospheric monitoring systems in the Pike River mine, leading to re-entry operations being suspended.
"If you can't explain it, you stop what you're doing until you can."
Little said this afternoon the unpredictable nature of the operation was expected, and information about the events of the last 12 to 24 hours is now being looked at.
The elevated oxygen levels might be because the monitoring equipment is inaccurate. Another possibility is that it oxygen was coming through the strata.
Little said the delay "could be days, could be weeks", but a safety priority meant that further action could not take place until more is known about the elevated oxygen levels.
"Yesterday unexpected and unexplained readings were reported by the atmospheric monitoring systems in the Pike River mine, leading to re-entry operations being suspended.
"Safety has always been our first priority, and will continue to be. In these circumstances the appropriate precaution is to temporarily suspend operations."
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 have 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 trapped miners.
