Drillers finished one ventilation borehole into Massey Energy's Upper Big Branch mining operation in Raleigh County and were working on another as workers tried to vent the mine of dangerous gases so the search for the still unaccounted-for miners could resume, The Charleston Gazette reported.
A third borehole is being planned, officials said.
"The odds are not in our favor because of the horrendous blast we had," Manchin said.
Two other miners remained hospitalized since being rescued Monday.
The U.S. Mine Safety and Health Administration, a unit in the U.S. Labor Department, said it appointed a team to investigate the explosion.
"Twenty-five hardworking men died unnecessarily in a mine Monday," said Labor Secretary Hilda L. Solis. "The very best way we can honor them is to do our job. MSHA's investigation team is committed to finding out what happened, and we will take action."
The team of mine safety professionals will "work tirelessly" to evaluate all aspects of the accident and determine its cause, Assistant Secretary of Labor for MSHA Joseph A. Main said in a release posted on the agency's Web site.
Gov. Manchin and congressional members said they also would investigate the explosion.
At the sprawling complex, rescuers were holding onto hope the four missing miners got to an airtight rescue chamber that had enough air and supplies for four days.
Kevin Stricklin, MSHA's coal administrator, said once rescue teams can get into the mine, it could take about two hours to get into the areas where the miners are believed to be located.
"They may not be in the exact location we think they are, so we may have to fan out a little bit," Sticklin said. "You have to play it by ear."
The mine explosion -- the worst in the United States since 1984 when 27 miners died in Utah -- brought the checkered safety record of Massey Energy into the spotlight. Several federal officials and miners suggesting that Monday's explosion might have been preventable, The New York Times reported.
Miners had been evacuated three times from the Upper Big Branch during the last two months because of dangerously high methane levels, two miners told the newspaper.
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