The search for six miners missing deep underground was abruptly halted after a second cave-in killed three rescue workers and injured at least six others who were trying to tunnel through rubble to reach them.

It was a devastating turn for the families of the six men trapped in the Aug. 6 collapse at the Crandall Canyon mine and for the relatives of those trying to rescue them. It's not known if the trapped miners are alive.

"It just feels like a really hard blow to swallow after all we've been through the last week and a half and everyone trying to hope in their own individual way," Huntington Mayor Hilary Gordon said in telephone interview Friday with a cable news network.

All rescue workers were evacuated from the mine Thursday evening and work underground was stopped. Asked if the search would be suspended, "that's something to be determined," said Rich Kulczewski, a U.S. Department of Labor spokesman.

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The cave-in at 6:39 p.m. was believed to be caused by what seismologists call a "mountain bump," in which shifting ground forces chunks of rock from the walls with great force. Seismologists say such a bump caused the Aug. 6 cave-in that trapped the six men more than 3 miles inside the central Utah mine. That led to the frenetic effort by rescuers to dig through the mine toward the men and drill narrow holes atop the mountain in an attempt to learn their whereabouts and perhaps drop down food and water.

It was not immediately clear where the rescuers were working or what they were doing when Thursday's bump occurred.

Underground, rescuers had advanced only 826 feet in nine days. Before Thursday's cave-in, workers still had about 1,200 feet to go to reach the area where they believe the trapped men had been working.

Mining officials said conditions in the mine were treacherous, and they were frequently forced to halt digging because of seismic activity.

A day after the initial collapse, the rescuers were pushed back 300 feet when a bump shook the mountain and filled the tunnel with rubble.

The digging had been set back Wednesday night, when a coal excavating machine was half buried by rubble by seismic shaking. Another mountain bump interrupted work briefly Thursday morning.

"The seismic activity underground has just been relentless. The mountain is still alive, the mountain is still moving and we cannot endanger the rescue workers as we drive toward these trapped miners," said Bob Murray, chief of Murray Energy Corp., the co-owner and operator of the Crandall Canyon mine.

On top of the mountain, rescuers were drilling a fourth hole on Thursday, aiming for a spot where devices called "geophones" had detected mysterious vibrations in the mountain. Both Kulczewski, the Labor Department spokesman, and Gordon, the mayor, said they believed that work continued after the accident.

"They're looking right now at finishing the drilling on the fourth hole, going through, and as I understood, that they're going to just be drilling the holes and ... putting the camera through and looking at these different ways to get in there, maybe through the top," Gordon told a cable news network. "But I don't think that they're going to be doing any mining down in the bottom again."

No details were available early Friday about the official cause of the rescuers' deaths. Their identities were not released. Injuries to the survivors ranged from cuts and scrapes to head and chest trauma.

Six of the injured were taken to Castleview Hospital in Price. One rescuer died there, one was airlifted to a Salt Lake City hospital, one was released and three were being treated, said Jeff Manley, the hospital's chief executive.

The second dead worker passed away at Utah Valley Regional Medical Center in Provo, hospital spokeswoman Janet Frank said. Another worker there was in serious condition with head trauma but was alert, she said.

The third death was confirmed by Kulczewski, the Labor Department spokesman.

Gov. Jon Huntsman flew to the hospital in Price early Friday and planned to meet with mine safety officials later in the day to discuss the future of the rescue operation.

Huntsman said he did not want underground tunneling to resume, but that the decision rested with the federal Mine Safety and Health Administration.

"We're pushing for that to cease right now unless MSHA and others can guarantee that it can continue safely," he said. "Whatever happens, we're going to want to ensure that it is done safely and that may take a little while.

"We as a state don't want any more injuries," he added. "We've had enough."

Before the latest cave-in, officials said the third of three holes drilled reached an intact chamber with potentially breathable air.

Video images were obscured by water running down that bore hole, but officials said they could see beyond it to an undamaged chamber in the rear of the mine. It yielded no sign the miners had been there.

Murray said it would take at least two days for the latest drill to reach its target, in an area where a seismic listening device detected a "noise" or vibration in 1.5-second increments and lasting for five minutes. The drilling began Thursday.

Officials say it's impossible to know what caused the vibrations and clarified the limits of the technology.

The geophone can pinpoint the direction of the source of the disturbance, but it can't tell whether it came from within the mine, the layers of rock above the mine or from the mountain's surface, said MSHA chief Richard Stickler.

The "noise," a term he used a day before, wasn't anything officials could hear, Stickler said. "Really, it's not sounds but vibrations."

Officials stressed that the motion picked up by the geophones could be unrelated to the mine, even as they drilled the new hole in an effort to uncover the source of it.