Rescuers expect to find 10 trapped miners soon.
They said a drill had reached a depth of 118 metres and was four metres short of the ceiling of a tunnel that leads to a hollow where the men may be located.
The tunnel is at the 10th level, or floor, in the mine.
"As soon as the drill head has reached level 10 we are hoping to get a camera and microphones down in 20 minutes," Mr Alfred Zechling, a spokesman for the rescue operation, told a news conference in Lassing, south west of Vienna. He said: "We hope to reach level 10 in the next few hours, but if we run into the slightest technical snag we are looking at a further delay. It will then take at least 10 to 12 hours before the first rescuer is sent down."
He said the camera, possibly mounted on a swimming robot, would be able to establish the fate of the men.
Rescuers were drilling through a filled steel tube 50cm wide and previously used for sending supplies into the mine. The tunnel with which the tube is linked leads to a so-called "dome" that may have served as an air pocket for the men.
"We hope as many as possible made it to the dome," Mr Zechling said.
Hopes of recovering the men alive, following the rescue of their colleague Mr Georg Hainzl on Sunday, were tempered by the knowledge that anyone who survived the massive mudslide could well have run out of oxygen by now.
The 10 were caught in a cave-in after they descended into the pit on July 17 in a failed attempt to find Mr Hainzl, aged 24, trapped by a smaller collapse in the magnesium silicate mine a few hours before. Mr Zechling said the seven-metre tunnel was probably filled with mud and water that would have to be pumped away. It was also possible that steel wreckage was in the way but it could be thrust aside by the drill head.
"If the tunnel is not completely blocked things will go relatively fast," he said.
Another, smaller hole drilled nearby had reached a depth of 55 metres. It would be used for sending down drinks and food to the men should they be alive, but drilling through the old steel tube proved to be quicker.