A collapse of a Utah coal mine that trapped six miners was so strong that seismologists initially thought it was an earthquake.

Ten miners were underground when a cave-in occurred at Genwal Mine in Huntington Canyon, but four were able to escape. At least 200 rescuers broke through walls of rock Monday to try to reach the six miners trapped 457 metres underground and about six kilometres from the mine's entrance, officials said.

Robert Murray, founder and chairman of Cleveland, Ohio-based Murray Energy Corp., holds a map as he talks about the six trapped coal miners at the entrance to his mine on Monday.
(Douglas C. Pizac/Associated Press)

It could take rescuers three days to try to free the men by drilling into the mine vertically from the mountaintop and horizontally from the slope, officials said.

Rescue crews have been unable to make contact and don't know whether they're alive. If they survived the collapse, they have enough air and water for several days, mine owner Robert Murray said.  

Genwal Mine, which is built into a mountain in the rugged Manti-La Sal National Forest some 225 kilometres south of Salt Lake City, reported the cave-in at 3:50 a.m. local time, about an hour after seismologists detected a shock wave of 4.0 magnitude.

There were conflicting reports about whether there had been a quake. Seismograph stations at the University of Utah recorded 3.9 magnitude, but scientists later concluded the disturbance was because of the mine collapse. The information was disputed by Murray, who claimed the epicentre was 1.6 km from the trapped miners.

Since the mid-1990s, at least a half-dozen other mine collapses have caused similar seismic waves, including a 1995 cave-in in southwestern Wyoming that caused readings as high as a 5.4 magnitude.

A command centre was being set up in Huntington City, about 24 kilometres from the mine, said Teresa Behunin, an accountant affiliated with the mine. She had no other details.

"Mine injuries and mine disasters are not uncommon unfortunately in this area," Ryan Faulk told CBC News.

There have been several mining disasters, including a methane gas leak at a mine that killed 30 people in 1990, he said.

With files from the Associated Press