Rescuers using a second hole drilled into a collapsed Utah coal mine so far have not established communication with six trapped miners.
The six men, who have not been heard from since the mine collapsed on Monday did not respond when rescuers tried to communicate by pounding on the drill, which pierced the mine ceiling.
A camera lowered into the second hole drilled into the Crandall Canyon coal mine in central Utah gave poor images of the space and would be cleaned and put back again, he added.
The second hole hit nearly on target and found what is called a 'survivable space'.
It will take crews digging horizontally four to five days to create an opening large enough to pull the miners out but if they are alive, the larger drill hole can be used to provide food, water and air until they are rescued.
Officials have said the men could potentially survive for weeks in an underground chamber if they were not killed by the initial collapse.
