Police Superintendent Gary Knowles said yesterday rescuers were keeping an open mind but officials and relatives were preparing for the worst.
"We are planning for all outcomes and, as part of this process, we're planning for the possible loss of life as a result of what's occurred underground."
Toxic gases have prevented rescuers from entering the mine, near Atarau on South Island, and there has been no contact with the men, including Pete Rodger, 40, from Perthshire, and Malcolm Campbell, 25, from St Andrews, Fife, since a fireball ripped through the Pike River mine in Atarau on South Island on November 19.
Drilling of a small shaft into the mine to test dangerous gas levels was expected to be completed yesterday, and experts were preparing a military robot to enter the mine to provide pictures and gas samples up to a mile down. Mr Knowles said that would give rescuers an idea of whether they can enter themselves.
Police have said the miners, aged 17 to 62, are believed to be about 1.2 miles (2km) down the tunnel. Each carried 30 minutes of oxygen, and more stored in the mine, along with food and water, could allow several days of survival.
Mine chief executive Peter Whittall said teams drilling the second borehole into the mine had reached a depth of 410ft (125m) but had hit hard rock.
Mr Campbell's father, Malcolm senior, 50, and mother Jane, 45, said they were clinging on to the hope of receiving some good news. "We can't concentrate on anything, we can't sleep because it's difficult. Our prayers and thoughts go out to everybody who is going through this in New Zealand. We just keep hoping that everything will be fine."
Mr Campbell is due to marry his fiancee, Amanda Shields, 23, next month.
His father said: "Only last month we were watching the Chilean miners being rescued. I remember saying to my wife how awful it would be if it happened to Malcolm and now it has."
Mr Rodger moved to New Zealand two years ago to be near his mother and sister. Friend John Daniel, 59, described him as an adventurer who loved life.
"I'm just shocked he is caught up in all this," he added. "Peter just wanted to make the most of his life and just took everything as it came."
New Zealand Prime Minister John Key said there is "every chance" the 24 New Zealanders, two Australians, two Britons and one South African are still alive and managed to find oxygen.
One of two workers who escaped described the explosion as "a shotgun blast, but much, much louder and more powerful".
Daniel Rockhouse, 24, was smashed into the mine wall before collapsing amid the smoky, swirling gas and dust. "I got up and there was thick white smoke everywhere – worse than a fire."
Mr Rockhouse, whose brother Ben remains underground, said. "I couldn't see anything, and it was dead quiet. I yelled 'Help, somebody help me!' But no-one came. There was no-one there."
He stumbled across unconscious Russell Smith, and dragged him to safety. They reached the surface two hours later.
29 saved from flooded pit
All 29 miners trapped in a flooded Chinese coal mine were lifted to safety yesterday.
The miners were trapped Sunday morning after the small, privately-owned Batian mine in south-western Sichuan province suddenly flooded.
China Central Television showed a line of ambulances and large crowds waiting near the entrance to the mine burst into cheers and applause as medics brought out survivors wrapped in quilts after being led out. The miners were barefoot and naked.