The search for six miners missing deep underground in Utah 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.
"We have suspended indefinitely the underground portion of this rescue effort," Richard Stickler, head of the US federal government's Mine Safety and Health Administration, said.
He said rescuers would continue to drill bore holes through the top of the mountain to find the miners, who have not been heard from since a collapse on August 6th.
One of those killed and one seriously injured in Thursday evening's collapse were federal employees, Mr Stickler said.
"Yesterday we went from a tragedy to a catastrophe," said Utah governor Jon Huntsman outside the Crandall Canyon mine as he called for new efforts to make mining safer in his state and the country.
The cave-in, which occurred about 6.35 p.m. MDT (0035 GMT), was called a "mountain bump" - an eruption of rock and coal under pressure from overhead rock as drilling removes surrounding rock and material shifts.
Seismologists at the University of Utah said they recorded waves from the bump "consistent with further settling and collapse within the mountain." It remains unclear what caused the first collapse. Mine owner Robert Murray has said it was triggered by an earthquake; geologists say it was not.
Central Utah has long been rich not just in coal deposits, but also the great fortunes and deep despair that come with pulling it from the ground. Monuments and museums to past tragedies mark the roads and towns in the center of the state.
The list of accidents stretches back at least to May 1900, when 200 men were killed by an explosion in the Winter Quarters Mine, one of the worst mining accidents in US history.