Rescue workers began drilling a hole Tuesday toward where they believe four miners may be located more than a day after a blast killed 25 others in a coal mine here.

"There's a sliver of hope, but we know that the odds are not in our favor," Governor Joe Manchin told CNN.

"Everyone's going to cling to the hope of a miracle," he told reporters. "That is the true agony of this."

One of four drills had already begun its 1,100-foot descent to open a 6-inch hole in a ceiling of the mine, said Chris Adkins, CEO of Massey Energy Company, owner of the Upper Big Branch South Mine where Monday's fatal blast occurred.

The drill was 160 feet down at 4 p.m. and was expected to penetrate the seam between noon and 2 p.m. Wednesday, Adkins said.

When it does enter, "there is always a risk" that the drill bit will ignite another explosion, he said. But rescuers were injecting water into the hole at the same time, lessening those odds, he said.

Another drill was located next to the first, he said.

"If one misses its mark, hopefully the other one will hit the mark," he said.

The process is made more uncertain because the drill can change direction when it enters a seam that has already been mined, he said. Two other drills were in place and expected to begin their downward journey by nightfall, he said.

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