Rescue workers struggling to reach 13 Russian miners trapped below ground since Thursday have drilled a hole into the mine shaft where they are believed to be stranded.
Rescuers will look for the men in special teams
No water came out of the shaft when the hole was bored, indicating the area was not completely flooded.
But there was also no sign of life from the group of men.
Despite succeeding in piercing the narrow 3.2 centimetre (1.2 inches) hole, rescuers remained three metres (10 feet) away from the area where it is hoped the miners may be marooned in an air pocket.
Emergency workers are now planning to use dynamite to blast a passageway 1.4 metres (4.6 ft) high and 2.5 metres (8.2 ft) wide to reach the men, French news agency AFP reported.
Three five-men teams of mine rescue specialists, who have been rehearsing their movements above ground, will then enter the tunnel, Russian news agency Interfax reported.
Rescue workers have remained cautiously hopeful the men will be found safe.
"Maybe we'll punch through and find them standing there alive," the head of rescue operations told the Associated Press news agency.
There has been no sign of life from the men - who have no food or water - since an underground lake spilled into the shaft where they were working.
Officials had expressed hope that air levels in the mine were sufficient for the miners to survive several more days despite rising carbon monoxide levels, Reuters news agency reported.
Rescuers were using powerful compressors to pump vital fresh air underground but by mid-afternoon local time this will no longer be possible.
Teams are also pouring rocks, metal and even railway sleepers into the damaged mine shaft to try to block the breach in its wall but they say the work is having only a limited effect.
A total of 46 miners were trapped in the accident at the Zapadnaya coal mine in Novoshakhtinsk, which cut off power and stranded the miners 800 metres (2,600 feet) underground.
Timeline of events
Thursday 23 October: Water leaks from an underground lake into a shaft where miners are working. At least 15 escape but 46 are trapped
Friday 24 October: Rescuers begin tunnelling from two neighbouring mines and try to stop water flow
Saturday 25 October: Emotional scenes as rescuers bring up 33 miners, but 13 are still unaccounted for
Monday 27 October: Rescuers continue to dig a "tunnel of hope" towards the remaining men but are hampered by rising water, a gas leak and uncertainty over the men's position
Tuesday 28 October: Rescuers drill a small hole into the shaft where men are thought to be but no signs of life are reported
Thirty-three men were brought out on Saturday to emotional scenes.
It is not clear why the 13 men remained underground but it appears rescue workers could not locate them when the initial rescue operation was launched.
Exhausted relatives of those still trapped remain outside the main shaft, wrapped in anoraks and fur hats against the cold as they awaited news of the men and prayed with local priests.
"What am I to do with my children?" one weeping woman asked Reuters as she clutched her daughter.
"He was our breadwinner."
The 13 who are still missing include mine director Vasily Avdeyev - who was on his first day in the job when the accident happened.
Accidents are frequent in coal mines in Russia and its ex-Soviet neighbour, Ukraine.
Apart from the natural hazards associated with the work, miners complain of deteriorating safety conditions.
A similar incident at Zapadnaya in February was blamed on a lack of maintenance work at the mine, which had led to the creation of the underground lake.
There were no casualties on that occasion.