Seismic bump

The trapped miners have not been heard from since the mine caved in on August 6.

Thursday's seismic tremor, known as a bump, is an eruption of rock and coal under increased pressure from overhead rock as drilling removes surrounding rock and material shifts in an area of the mine.

The Salt Lake Tribune reported on its website that three ambulances went to the mine shortly after 7pm (0110 GMT), followed by three helicopters.

Ongoing efforts

Robert Murray, co-owner of Crandall Canyon Mine, said earlier in the day that the cavity found by a third bore hole had enough oxygen to sustain life indefinitely and that his crews would keep up efforts to contact the missing men.

Rescue crews were preparing to drill a fourth hole into the mine on Thursday.

However, work on a tunnel that could eventually get them out was proceeding slowly because of the seismic activity.

It is not yet clear what caused the mine to collapse.

Murray has said it was triggered by an earthquake despite disagreement from geologists.