Rescue crews drilling into a mountain to bring air and food to six trapped miners were two-thirds of the way to their target with one of two holes late on Wednesday, officials said.
A 6.35cm hole was drilled to 305m by late Wednesday night, said Lane Adair, general manager of the Crandall Mine, where the men were caught in a collapse early on Monday.
The miners were believed to be in an area 460m below ground, said Bob Murray, chairman of Murray Energy Corp, part-owner of the mine.
The smaller hole was 267m down on Wednesday evening, more than halfway to its target, said Bob Murray, chairman of mine co-owner Murray Energy Corp.
Crews could break through in 48 hours or less, the company said.
"Obviously we're dealing with the unknown," Murray Energy vice president Rob Moore said, referring to the potential for equipment breakdowns and dangerous ground shifts.
The larger hole, nearly 23cm in diameter, could be used to move provisions to the workers. That drill had reached just 30m by Wednesday evening, Adair said.
The bigger drill was faster and was expected to catch up, Moore said. Two holes were being drilled in case one is unsuccessful
"Everything humanly possible has been and is being done to rescue these miners," said Murray, who wore a miner's helmet during a briefing with reporters.
Murray offered no estimate on how long the miners could survive -- if they are still alive -- but backed off a claim Tuesday that they could subsist for perhaps weeks on available air.
"The oxygen depends on the size of the cavity they are in, and I have no idea what size that cavity is," he said.
Nothing has been heard from the men since the cave-in, not even the hammering on the ceiling that miners are trained to do in an emergency.
Only one miner has been identified. The men range from one miner with three weeks on the job to others with 10 years' experience, mine safety manager Bodee Allred said. Three of them are Mexican citizens.
Murray spoke to reporters on Wednesday after meeting with the miners' families at a school in Huntington, 16km away. At one point, he left the building, paced outside and returned.
Maria Buenrostro, the sister of trapped miner Manuel Sanchez, 41, said Murray got angry with relatives' questions and walked out. She also said there was no interpreter for three Spanish-speaking families.
"We want the truth, that's all we want," Buenrostro said. "If there's nothing that they can do about it, you know, just tell us so we know what to expect when they bring them out."