TALLMANSVILLE, W.Va. (AP) – Rescuers pushed deeper into a mineshaft in a desperate search for 13 trapped coal miners Tuesday, but the prospects of finding anyone alive appeared bleak after holes drilled into the ground yielded deadly levels of carbon monoxide and no signs of life.

Gov. Joe Manchin urged West Virginians to “believe in miracles,” and added: “It’s going to take a miracle, I think.”

The men, trapped 260 feet down by an explosion Monday morning in the Sago Mine, were believed to be about 12,000 feet past the opening of the shaft. By midday Tuesday, more than 30 hours after the blast, rescue teams had penetrated 10,200 feet, working their way on foot for fear machinery might cause volatile gases to explode.

“We will push forward as quickly as we can as long as there is a shred of hope that we can get our people out safely,” said Ben Hatfield, chief executive of mine owner International Coal Group Inc.

President Bush said the nation was praying for the men, and he offered federal help to bring them out alive. “May God bless those who are trapped below the earth,” Bush said from the White House.

Earlier in the day, rescuers drilled narrow holes into the mine, inserted air monitors and found levels of carbon monoxide more than three times the maximum regarded as safe. Carbon monoxide, a byproduct of combustion, can be lethal.

Hatfield said it was possible the miners barricaded themselves somewhere and were still alive. But he said: “We are very discouraged by the results of this test.”

There was more discouraging news: A camera was lowered down a 6 1/4-inch hole but spotted no sign of the miners. Also, drilling crews pounded on a steel pipe and listened for a response from the trapped men, but heard nothing, Hatfield said.

“They repeated this process several times over a 10-minute period, but the drill crew heard no response,” Hatfield said.

Upon hearing the discouraging news, family members retreated to the nearby Sago Baptist Church without making any comments. Hundreds had spent the night huddled in tents or wrapped in blankets in the cool, damp air.

“That don’t sound good,” said a red-eyed Donald Marsh, who kept an all-night vigil across from the mine where his half-brother, Jim Bennett, was trapped. Still, Marsh said he was unwilling to let go of all hope.

“Obviously, it was devastating,” said Nick Helms, whose 50-year-old father, Terry, was among the missing. But Helms said his father once told him that mine air tests could be deceiving because safer air could be just a short distance away.

“My father and every person who goes into that mine knows what they’re doing. I’m sure they found a way to stay safe,” he said. “I just want to see him again.”

At first, rescue crews moved slowly through the shaft, because they had to stabilize it and repair the roof as they went along. But on Tuesday, officials said, the rescuers realized they had no time to waste and abandoned that approach.

The Mine Safety and Health Administration had rescue and safety specialists on the scene, set up a command center and brought in a robot capable of exploring areas too dangerous for humans. But the robot was abandoned after it became bogged down in the mud.

The cause of the explosion about 100 miles northeast of Charleston was under investigation. Coal mine explosions are typically caused by buildups of naturally occurring methane gas. And Manchin spokeswoman Lara Ramsburg said earlier that it may have been sparked by lightning.