Chile's mining minister announced that a shaft wide enough to provide an escape for 33 trapped miners should reach the men by tomorrow - and that their rescue could begin anywhere from two to 10 days after that.

Once the drill breaks through to the miners' cavern some 2,000 feet underground, the time frame for the rescue will be determined by a technical evaluation of the risks involved, Minister Laurence Golborne said, meaning they could be pulled out as early as Monday or Tuesday.

The countdown hinges on whether the rescue team decides to use steel piping to line the walls of the shaft and reduce the risk of a rock fall or other obstruction jamming an escape capsule that will carry the miners up, Mr Golborne said.

But inserting straight pipe with walls of half-inch-thick steel through a curved and fractured section of the shaft also risks clogging the hole or knocking rock loose. If sections of pipe break apart or get stuck, it could slow the rescue.

The alternatives are leaving the raw "live rock" unreinforced, inserting a sleeve in the top section only, or encasing the entire shaft, a process that would delay the rescue for another 10 days after the decision is made.

"They are all possible alternatives," Mr Golborne said. "There are risks and benefits we have to think about."

Mr Golborne said a decision will be based on technical factors once a video camera is lowered to thoroughly examine the shaft's walls.

While the Plan A and Plan C drills have been slowed by efforts to keep them on target, Plan B resumed with fresh bits carving through the final 300 feet.