Rescuers had been making their way to the area where the miners were believed trapped at Massey Energy Co's sprawling Upper Big Branch mine, where the blast occurred around 3 pm (1900 GMT) yesterday. However, safety officials said at a news conference that the search was suspended because rising methane gas levels in the mine made it a high risk for another explosion.

Earlier, Kevin Stricklin, an administrator for the federal Mine Safety and Health Administration, said officials hoped some of the missing had survived the initial blast and were able to reach airtight chambers stocked with food, water and enough oxygen for them to live for four days.

However, rescue teams made it to one of two nearby shelters and it was empty. The gas levels prevented them from reaching the second.

Massey Energy and safety officials confirmed that 25 bodies were found. The death toll had risen from seven earlier in the day to 12 at about midnight. A total of 29 miners were in the area when the blast happened, he said.

"It does not appear that any of the individuals made it to a rescue chamber," Stricklin said at a news conference. "The situation is dire."

State mining director Ron Wooten said though the situation does not seem promising to reach the four still missing, rescuers wouldn't give up.