Toxic gases have prevented rescuers from entering the mine and there has been no contact with the missing men. Two workers were able to stumble out of the mine within hours of the explosion.
Monday, drilling of a small shaft into the mine to test dangerous gas levels is expected to be completed.
Experts are preparing a military robot to enter the mine and take pictures, once the air quality question is resolved. Built up methane gas is the suspected cause of the explosion, though officials said that may not be confirmed for days.
The Associated Press contributed to this story.