HUNTINGTON (AFP) - Efforts to establish contact with six miners buried in Utah made painstaking progress on Thursday as a giant drill bored slowly through mountain rock towards the men, officials said.
Rescuers have been toiling relentlessly to reach the men, who have not been heard from since a tunnel they were working in at the Genwal Mine in Crandall Canyon, 200 kilometers (120 miles) southeast of Salt Lake City, collapsed at around 3:50 am (0850 GMT) Monday.
A round-the-clock operation has seen rescuers drilling through the mountainside in a bid to set up communication shafts that could improve ventilation and allow for food and supplies to be lowered to the men.
Robert Murray, a director of Utah American Energy that owns and operates the mine, said earlier that a 6.5-centimeter (2.5 inch) shaft to the cavity where the men were could be completed by around 5:00 pm local time (2300 GMT).
However Murray told reporters later Thursday that the drill was making slow progress and was still several hours away from reaching the men.
In an interview with CNN, Murray said rescuers hoped to know whether efforts to bore through to the miners had been successful "in a matter of hours."
"It will be soon ... I hesitate to give an exact hour," Murray said.
Richard Stickler, head of the Mine Safety and Health Administration, said the drill had reached a depth of 527 meters (1,730 feet) and was around 43 meters (140 feet) from the men. The drill was moving at a rate of around six meters (20 feet) per hour.
Murray warned earlier it would still take several days before a separate rescue team was able to clear enough rubble and physically extract the men.
He also cautioned it was possible the drill might strike a coal seam rather than the cavern where the men were. If that happened, the drilling would have to start again, he said.
"We may not come out in the mine in the position where we want to be. We might hit a solid pillar and have to start all over again," he said.
If the drill struck the cavern, communication devices would be lowered down the shaft to the workers he said.
A second 21.5 centimeter (8.5-inch) diameter drill carving out a shaft which could be used to deliver food and water could reach the workers sometime on Friday, Murray added.
Mine safety manager Bodee Allred said Wednesday he had not given up hope of finding his co-workers alive.
"I have full faith they are in there alive and breathing," Allred said.
The six men were believed to be located in a chamber around 450 meters (1,500 feet) underground.
While Murray has remained adamant that Monday's cave-in was caused by an earthquake, the US Geological Survey said in a statement that the collapse was responsible for seismic readings that initially suggested a 4.0 quake.
"The event picked up does not appear to be an earthquake," the USGS statement said. "Primary analysis of the waves and location suggest that it was a mine collapse and not an earthquake."
The Utah drama has revived memories of the doomed effort to reach 13 miners who were trapped after an explosion at the Sago Mine in West Virginia in January 2006.
Twelve miners died and only one survived after being buried underground for 41 hours.