Gas levels are still too volatile for rescuers to enter the New Zealand mine where 29 men are trapped following an explosion two days ago.
Specialist search and mine rescue staff and other emergency services will remain on site at the Pike River Coal mine overnight as monitoring of air and gas levels continue.
New Zealand Mines Rescue general manager Trevor Watts said a rescue team is poised at the mine ready to go in when tests show the smallest window of opportunity.
Mr Watts told a media conference in Greymouth on Sunday afternoon that poisonous gas levels are being tested every half hour but it is still too volatile to enter the mine.
He said although gas levels are generally coming down they are fluctuating.
Mr Watts said that one of the mines rescue team is one of the men who is trapped.
"Every mines rescue member that is working on this operation is waiting to go underground to rescue our brothers, the whole lot of them are our brothers", he said.
Mr Watts said once rescuers were given the all clear it could take about two hours to reach the men by foot, carrying heavy equipment and wearing breathing apparatus.
He said after an initial reconnaissance rescuers would then have to withdraw and return to a fresh air base that would be established on the surface of the mine.
Mr Watts and the police officer in charge of the mine rescue, Superintendent Garry Knowles, say they are still conducting a rescue operation.
There has been no communication with the miners and contractors at the horizontal mine at Atarau near Greymouth since a methane gas explosion cut power and blew out ventilation fans about 3.45pm on Friday.
The men are believed to be trapped about 2km along the Pike River Coal mine tunnel burrowed in rugged mountains and bush and about 150 metres below the surface.
But the situation remains too dangerous for rescuers to enter the mine due to an underground fire and the threat of toxic fumes.
Pike River Coal chief executive Peter Whittall told a news conference on Sunday morning tests show there is some combustion of material in the mine.
Mr Whittall said it is difficult to know what sort of fire it is. It may be smouldering coal, rather than large flames, but it is generating heat and gases including methane and carbon monoxide.
"It's most likely coal, but it could also be oils or something else underground that is smouldering just enough to give off these gases."
Hole drilled to take air samples
Contractors were expected to begin drilling a small bore hole up to 150 metres deep on Sunday to reach one of the open areas inside the mine.
The best case scenario is that this will take 16 hours, but if they strike any problems it could take 24 hours.
The 15cm hole will be used primarily to take air samples but could also be used for items, including a camera, but only if what is sent down is electronically safe and will not set off another explosion.
It will also allow rescuers to hear anyone talking.
Fresh air continues to be pumped into the mine through a shaft.
On Sunday a mining rig was put in position to drill a new air hole into the mine.
Families taken to mine
Family members of some of the workers were taken to the mine on Sunday morning to help them understand the situation rescuers are facing.
Access has been restricted since the explosion and it is the first time family have been allowed through the cordon.
Two men walked out of the mine unaided on Friday and have been discharged from hospital.
Sixteen of the trapped workers are employed by Pike River Coal, while 13 are local contractors. The youngest of the miners is a 17-year-old New Zealander, while the oldest is 62.
Police have confirmed the nationalities of the workers. There are 24 New Zealanders, two Australians, two British citizens and one South African.
The coal miners' union is calling for authorities to release their names.