HUNTINGTON, Utah -- There has been a setback in the effort to free six trapped miners from a Utah coal mine.

Rescuers have been slowed by falling rock and debris. Workers have been unable to make significant progress and the initial effort is being declared a failure. A part owner of the Crandall Canyon mine says he's very disappointed.

Searchers have been unable to contact the miners. It's not clear if the six are dead or alive. If they survived, a company official says there should be enough air and water to last several days.

Rescuers plan to spend the night bulldozing a road outside the mine to make way for a drilling rig that can punch holes large enough to improve ventilation and determine whether the men are alive.

They also plan to continue drilling from inside and outside the mine.

The miners are believed to be about four miles from the mine entrance. Hundreds of rescuers are working to free the men by drilling into the mine vertically from the mountaintop and horizontally from the side.

Robert Murray, the chairman of Murray Energy, a part owner of the Crandall Canyon mine, said, "We're going to get them."

Murray Energy does contract work at the mine, which is large enough to accommodate trucks. But Murray said rescue crews don't know how much rubble is in the way.

"There is nothing on my mind right now except getting those miners out," Murray said.

University of Utah seismograph stations recorded a seismic waves of 3.9 magnitude early Monday, causing speculation that a minor earthquake had caused the cave-in. Scientists later realized the collapse at the Genwal mine had caused the disturbance.

"There is no evidence that the earthquake triggered the mine collapse," said Walter Arabasz, director of the seismography stations.

The mine reported a "cave-in" at 3:50 a.m., the Emery County sheriff's office said.

"Rescue workers are on scene trying to locate six miners that are unaccounted for," the sheriff's office.

Rocky Mountain Power, a utility with a power plant in the area, sent a rescue team and heavy equipment to the mine, about 140 miles south of Salt Lake City, spokesman Dave Eskelsen said.

A command center was being set up in Huntington, about 15 miles from the mine, said Teresa Behunin, an accountant with Utah American Energy, which owns the mine. She had no other details.

The sheriff's office had said earlier there were no immediate reports of damage or injuries blamed on the quake, centered under the Huntington Canyon area, about 100 miles southeast of Salt Lake City.

Emery County has had at least one prior mine disaster, when, in 1984, a fire in the Wilberg mine killed 27.

Neighboring Carbon County also has had three notable disasters. In 2000, two men died during an explosion at the Willow Creek mine; a 1924 explosion took 172 lives at the Castle Gate mine; the Scofield mine disaster of 1900 claimed 200.

Emery and Carbon counties were originally one county until the territorial legislature split them in 1894.

According to the state of Utah, the mine is projected to be one of the smallest producers of coal in the state in 2007 at 625,000 short tons.

Utah ranked 12th in U.S. coal production in 2006. It had 13 underground coal mines in 2005, the most recent statistics available, according to the Utah Geological Survey.

At least a half-dozen other mine collapses since 1995 have caused similar seismic waves, including one in southwestern Wyoming that caused readings as high as 5.4 on the Richter scale.