Police said they remained "optimistic" over the fate of 29 miners including two Scots missing after an explosion in a New Zealand coal pit.
However they warned that they were "planning for all outcomes" and possible loss of life.
Pete Rodger, 40, from Perthshire, and Malcolm Campbell, 25, from St Andrews, Fife, are missing after a fireball ripped through the Pike River mine in Atarau on South Island.
Rescue teams have still not entered the mine, more than three days after a debris-laden blast tore through the pit's underground tunnels.
Police Superintendent Gary Knowles told a news conference today: "We still remain optimistic and are keeping an open mind, but we are planning for all outcomes and the possible loss of life as a result of what has happened underground.
"We remain positive and we are going forward until we get a result."
Officials were today drilling a 500ft (152m) hole from the mountain above the mine to assess air quality and to lower listening devices.
A hi-tech robot was also being prepared to be sent into the mine to transmit pictures and take more measurements.
Police said there was still too much combustible and noxious gas present for rescuers to enter safely, despite fresh air being pumped down the mine through an open air line.
Mr Knowles said: "The situation remains grave, given we've had no contact from the men for more than three days.
"This is a search and rescue operation. We're basically going to go in there and bring these guys out."
Mine chief executive Peter Whittall said that teams drilling a second borehole into the mine had reached a depth of 410ft (125m), but the operation had been slowed due to reaching 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 about their son.
They told STV 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 told the Mail on Sunday: "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 who emigrated there.
His New Zealand-born girlfriend, Dianne Morris, wrote on Facebook: "Just got to keep having positive thoughts."
Mr Rodger's friend, John Daniel, 59, told the Sunday Telegraph he was 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.
He said: "The advice I have is that there is oxygen in the mine and there is every chance that those miners have managed to get to a pocket of that oxygen flow and therefore that they are alive."
One of two miners to escape the blast described being bombarded with a wall of dust and debris.
Russell 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.
"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.
Colleague Daniel Rockhouse pulled him to safety and, when he regained consciousness, the pair took at least an hour to walk out of the dust-choked tunnel.
The missing men, aged 17 to 62, are believed to be about 1.2 miles (1.9km) down the main tunnel.
Prime Minister David Cameron and Prince William have sent messages of support and Scotland's First Minister Alex Salmond told BBC Reporting Scotland: "We are concerned obviously for the fate of all 29 of the miners who are trapped.
"But the fact that two Scots are among them and two Scottish families have that immediate concern makes that all the more immediate for people across Scotland.
"But there's no more we can do than send our best wishes for rescue."
Pike River has operated since 2008, mining a seam with 58.5 million tons of coal, the largest-known deposit of hard coking coal in New Zealand, according to its website.
The mine is not far from the site of one of New Zealand's worst mining disasters - an underground explosion in the state-owned Strongman Mine on January 19, 1967, which killed 19 workers.Reuse content