Rescue efforts have resumed at a coalmine in the US state of Utah, where six men have been trapped underground since Monday after it collapsed.
The miners are trapped some 1,500ft below the surface
Two holes are being drilled to bring them air, water and food. No contact has been made with the men, who are 1,500ft (457m) underground.
The furthest of the holes has so far reached a depth of 1,000 ft, mine official Lane Adair said.
The head of the mine said it could take at least a week to bring the men out.
It is unclear how much air is in the mine, although it is reported to be stocked with drinking water.
CRANDALL CANYON MINE
Located in Manti-La Sal National Forest, 16 miles (25km) from Huntington
Uses the "retreat mining" method, which experts say is one of most dangerous
Coal pillars hold up area of mine's roof. When completely mined, pillars are pulled, causing intentional roof collapse
Rescue teams had earlier suspended their efforts because of rock falls on Tuesday.
Seismic shocks wiped out a 310ft advance made by rescuers, taking them "back to square one", said Robert Murray, chairman of Murray Energy Corp, which owns the mine.
The two drill holes are expected to reach the miners by Thursday or Friday night, he added.
Rescuers had initially hoped to reach the miners via an adjacent mine shaft, but were forced to withdraw after moving just 50ft because of "geological and geotechnical problems".
The group is thought to be 3.4 miles (5.5km) from the mine entrance.
According to Mexico's consul in Utah, three of the miners are Mexican citizens.
It is still not clear what caused the cave-in at the mine, 140 miles (225km) from Salt Lake City.
Initially the collapse was blamed on an earthquake, but experts have since suggested the shafts might have caved in with enough force to register on seismographs.
Relatives are waiting anxiously for news of the six men
This has led to speculation mining procedures could have triggered the incident.
It has been claimed the workers were using a risky technique known as "retreat mining", where the last standing pillars of coal are pulled down and the roof is allowed to fall in.
But Mr Murray has rejected this, saying an earthquake caused the collapse.
"The damage in the mine was totally unrelated to any retreat mining," he said.
"This was caused by an earthquake, not something that Murray Energy... did or our employees did or our management did," he said.
US federal mining inspectors have issued 325 citations for alleged safety violations at the mine since January 2004. Of those, 116 were considered "significant and substantial" and likely to cause injury.
Experts have said the number of citations is not unusual, and the mine's owners say they run a safe mine.