Mining officials in the U.S. state of Utah say a second, wider drill has broken through to the chamber more than 550 meters underground where six men are believed to be trapped.
Officials say they hope the larger shaft will allow cameras to look into the cavity for signs of life. The larger hole is also wide enough to accommodate food and water.
The mine owner said Friday a small drill had reached the chamber where the men were believed to be trapped, but a microphone detected nothing but silence, and air quality readings suggested there was not enough oxygen to sustain life.
It could still be several days before rescue workers reach the miners, who have been trapped in the mine since Monday.
It is not clear whether an earthquake caused the mine to collapse or if seismic activity within it contributed to the cave-in.
Some information for this report was provided by AP.