Rescue crews worked through the predawn darkness on Tuesday on ways to find six miners trapped 1,500 feet underground after a coal mine collapsed in central Utah.

Dangerous conditions, including falling rock, ended the first drilling effort to save the workers at Crandall Canyon Mine on Monday night.

Every initial effort at rescue has failed, said Robert Murray, president of Murray Energy, which owns the mine operator.

The mine caved early Monday with such force that U.S. geologists are investigating whether it accounted for an earthquake registered nearby around the same time.

There has been no sign of life from the workers since the collapse more than 24 hours ago.

Rescue teams spent the night clearing a road outside the mine to allow a large drilling rig to get through on Tuesday, local television reported.

We will be here on our feet until we get these men out one way or the other, Murray told reporters.

Family members of some of the trapped men were waiting out the night at the Huntington Senior Center, according to A.J. O'Neil of the Emery County Sheriff's office.

They're gathered there, he said early on Tuesday. We haven't had any updates.

It was not known what caused the collapse.

The U.S. Geological Survey reported a magnitude-4 earthquake near the mine at the time of the cave-in. It was analyzing data to determine whether the shaking was produced by the collapse itself.

If you have a mine collapse, there will be a seismic component, said Harley Benz of the USGS' National Earthquake Information Center. We simply don't know at this point.

For some, the incident brought back memories of the 1984 Wilberg Mine disaster, which killed 27 miners in the worst coal-mine fire in Utah history.

The area in central Utah, about 140 miles south of Salt Lake City, is known for its mining industry and has seen its share of tragedy.

All we can do is wait and pray and let the rescuers do their job and until we hear, we will continue praying with the families of the missing miners, Brad King, a Utah state representative from nearby Carbon County, said on Monday.

Concerns about mine safety in the United States resurfaced last year when 12 miners were killed in an explosion at International Coal Group's Sago mine in West Virginia.

In response, Congress passed the Mine Improvement and New Emergency Response Act, which President George W. Bush signed into law last year.

(Additional reporting Doina Chiacu in Washington)