Toxic gases after Friday's explosion still prevented rescuers from entering the mine on Sunday, and evidence of heat underground was concerning officials, who feared there could be another blast.
"Something is happening underground, but what it is we don't know," said Peter Whittall, chief executive of Pike River Mine Ltd.
Fresh air was being pumped down an open air line, but gas levels were still fluctuating to an extent that waiting rescue teams were not allowed to enter the mine near Atarau on South Island.
A six-inch-wide hole was being drilled from the mountain above down 500 feet to the mine to assess air quality and to lower listening devices.
The missing miners have not been heard from since the blast but officials insist the search for them is a rescue operation.
Two Scots are amongst those who were in the mine at the time of the explosion. Yesterday, the father of one of them, Malcolm Campbell, called for rescuers to speed up their attempts to enter the mine.
Survivor Russell Smith was an hour late for work on Friday and was consequently not deep in the mine. He and fellow survivor Daniel Rockhouse walked out of the tunnel more than an hour after the explosion.
Mr Smith told New Zealand's TV3 news that he was driving a loader into the mine when he saw a flash in front of him.
"It wasn't just a bang, finish, it just kept coming, kept coming, kept coming, so I crouched down as low as I could in the seat and tried to get behind this metal door, to stop getting pelted with all this debris," Mr Smith said.
"I remember struggling for breath. I thought at the time it was gas, but ... it was dust, stone dust, I just couldn't breathe. And that's the last I remember," he said.
Mr Rockhouse pulled him to safety, and when he regained consciousness the two took at least an hour to walk out of the dust-choked tunnel.
Both were treated at a hospital for minor injuries.
"I could have easily been blown to bits," Mr Smith said, acknowledging he was lucky to have survived.
He said he couldn't help worrying about his colleagues still underground.
"There's a lot of young guys down there. A lot of people waiting," he said. "Whether they're still alive or dead or ... in an air pocket, you just don't know, because we're not too sure where the explosion was."
Anguished relatives of the 29 missing miners were given a tour of the site in order to better understand the situation, but the emotional tour did little to allay their concerns.
"It was good to see the layout of the place, but it's still hard," said Laurie Drew, whose 21-year-old son, Zen, is missing. "We just want to be there when they walk out."
Police have said the miners, aged 17 to 62, are believed to be about 1.2 miles down the main tunnel.
Officials believe the blast was most likely caused by coal gas igniting. An electricity failure shortly before the explosion may have caused ventilation problems that let gas build up.