HUNTINGTON - As many as a dozen mine rescue teams worked feverishly Monday night and into this morning, hoping for signs of life from six men trapped underground in the Crandall Canyon coal mine that collapsed earlier in the day.

But hopes were deflated - at least temporarily - when what had been called one of the most promising approaches to retrieving the miners failed.

Rescue workers had breached a seal on an old tunnel Monday afternoon they hoped would bring them within 100 feet of the miners. But their attempt to take a parallel tunnel deep into the mountain and then cut across the soft coal wall had to be scrapped when workers found multiple areas where the parallel tunnel had caved in.

It marked a dispiriting end to a day that began early Monday, when the collapse sent four miners scurrying for their lives and left six others trapped about 3.4 miles from the mine entrance. The workers have not been heard from since 2 a.m. Monday.

Robert E. Murray, CEO and president of the mining operation's parent company, Murray Energy Corp., acknowledged the setback but remained hopeful.

"We have no idea whether the damage in the mine extended to the area where the miners are," he said, noting rock and coal could have crushed the miners during the collapse, but he hoped it had simply sealed them off in a large space with plenty of air.

Earlier Monday, reports of an earthquake in the area of the mine had experts and operators speculating that the quake caused the collapse. But Utah seismologists believe the 3.9 reading more closely resembled an implosion. In other words, that the collapse created the seismic event.

However, Murray said Monday evening that he believed an earthquake caused the collapse, citing aftershocks recorded an hour afterward.

The Associated Press reported Monday that the trapped miners were performing a dangerous form of extraction called "retreat mining," in which coal pillars in mined-out tunnels are removed, often collapsing the ceiling. Bruce Hill, president of UtahAmerican Energy Inc., a Murray subsidiary that operates and co-owns the mine, defended the practice in an interview with the AP.

"It's been done for the last 70 years and been very successful for those years," Hill said. "It's something that the government approves and signs off on. Coal operators have been able to prove it's safe all along."

But Doug Johnson, an official with Murray Energy, denied the workers were using the technique. Asked about retreat mining by The Salt Lake Tribune on Monday night, Johnson said the miners were engaged in continuous mining where a machine with huge teeth tears into the back wall of a tunnel.

Murray described the area where the men were working as having 8-foot ceilings, and an 18-foot width, with a "comfortable" temperature of 58 degrees. The miners' only source of illumination would be the lamps attached to their hard hats, which they are trained to ration to extend the amount of time they'll have with light in an otherwise pitch-dark space.

Rescuers are now focusing on the 1,700 feet of shaft between the rescuers and the area where the miners were working. Murray said he does not know whether the rubble extends the entire 1,700 feet.

"We'll get them back," he said, "but it may be as much as three days."

Heavy equipment streamed in all day Monday on tractor-trailers from other mining operations as miners from Utah American Energy Inc. set out a four-pronged strategy to rescue the men, whom the company refused to identify. However, family members identified two of the workers as Kerry Allred and Mario Sanchez.

Family members spent most of the day awaiting word of their loved ones' fates at a senior center in Huntington. Murray said he has been in constant contact with them, and said they are "doing very well considering the circumstances.

"These folks are very strong," he said. "They're as good a group as I've ever seen."

Murray said the six men range in age from 20s to late 40s. They all are from the area, he said, and all "are family men."

The four miners who escaped the collapse went back in after their co-workers, but were unable to reach them.

"They donned their rescue gear and went into where the coal had sloughed off and saw they couldn't get in any farther," said Murray Energy official Doug Johnson.

Rescuers today will continue to seek passages inside the mine that will lead to the trapped miners. But along with those efforts, company officials described three different efforts to reach the miners from the mine's exterior.

A helicopter will help aim a large drill this morning that will burrow in from the top of the mountain. That method will take three days to reach the miners, Murray said. Bulldozers, he added, are also cutting roads for a second drill that might reach the miners in two days.

Another drill is boring horizontally into the mountain but there was no timetable on when that could prove successful. And Johnson noted that the shafts would not be big enough for an escape.

"It would be to only to determine signs of life," he said.

Gov. Jon Huntsman Jr. visited the mine site and the families of the trapped miners Monday afternoon.

"Everything that can be done is being done," the governor said. "They've deployed all the experts in the country."

Monday evening about 200 miners were involved in the rescue effort. They will work around the clock to rescue the miners.

The governor echoed the thoughts of mine officials, saying, "You have to be optimistic."

Earlier Monday, CEO Murray said "there was a good chance" to get the miners out. Later, he called it a 50 percent chance.

"I'm hoping and praying. There is a very good chance we'll find them in good condition."

The CEO said he, too, had been trapped in a mine.

"I take the safety of my employees to bed every night," he said. "There is nothing on my mind right now but getting those men out."

One miner arriving for duty Monday evening to aid the effort said he had been in the Crandall Canyon mine on a number of occasions and believed it to be safe.

"I was kind of shocked," said Jeremy Behling when he had learned of the collapse.

But miners know hazards exist, said Brian Powell, who also was going on shift Monday evening.

"There are a lot of other lines of work," he said. "But the pay is good and it's something I enjoy."

The trapped men were in the eighth hour of a 12-hour shift, said Johnson.

-- Matthew D. LaPlante contributed to this story.