TALLMANSVILLE, W.Va. – After waiting almost 12 agonizing hours for dangerous gases to clear, rescuers yesterday entered a coal mine where 13 miners were trapped underground after an explosion that may have been sparked by lightning.

The condition of the miners was not immediately known. Four co-workers tried to reach them but were stopped by a wall of debris, and the blast knocked out the mine’s communication equipment, preventing authorities from contacting the miners.

It was not known how much air they had or how big a space they were in. The miners had air-purifying equipment but no oxygen tanks, a co-worker said.

The first of eight search-and-rescue teams entered the Sago Mine, more than 11 hours after the blast trapped the miners. Rescue crews were kept out of the mine for most of the day while dangerously high levels of carbon monoxide – a byproduct of combustion – were vented through holes drilled into the ground, authorities said.

Company officials believe the trapped miners were about two miles inside the mine, about 260 feet under the ground. The crew entered the mine on foot for fear of sparking another explosion.

“You just have to hope that the explosions weren’t of the magnitude that was horrific from the beginning,” Governor Joe Manchin said on CNN. He added: “There are places they can retreat in all these mines, they have catacombs.”

The federal Mine Safety and Health Administration sent a rescue robot to the mine, situated about 100 miles northeast of Charleston.

About 200 co-workers and relatives of those trapped gathered at the Sago Baptist Church, across the road from the mine. Anna McCoy said her husband, Randall, 27, was among those missing. She said he had worked at the mine for three years “but was looking to get out. It was too dangerous.”

Coal mine explosions are typically caused by buildups of naturally occurring methane gas, and the danger increases in the winter months, when the barometric pressure can release the odorless, colorless, and highly flammable gas.

A Manchin spokeswoman, Lara Ramsburg, said the blast may have been sparked by lightning from severe thunderstorms. But Roger Nicholson, who serves as general counsel for the mine’s owner, International Coal Group, said that it was not clear what caused the blast and that there was no indication it was methane-related.

The mine has a single entrance, and the shaft winds its way for miles underground. The miners were supposed to be working about 160 feet below the surface, said the wife of one of the trapped men. But it was unclear how far into the shaft they had gone when the blast struck.

A senior vice president at ICG, Gene Kitts, said the company was preparing to drill into the mine to reach the miners.

“If the miners are barricaded, as we hope they are, they would prepare themselves for rescue by rationing,” Mr. Kitts said. The miners would probably have only their lunches and water on hand.

“These miners are experienced, they are well-trained,” Mr. Kitts said. “We are just praying they had an opportunity to put their training to use.”

The miners had three to 30 years of experience working in the mining industry, Mr. Kitts said. The company declined to release their names.

The blast happened between 6 a.m. and 6:30 a.m. as the first shift of miners entered to resume production following the holiday, Ms. Ramsburg said.

“As they were heading in, the car in the back either heard or felt some type of explosion. They headed back out. The first car never made it back out,” she said.

Thirteen miners were trapped, the coal company said. Four co-workers tried to reach the missing miners but “came to a wall” of debris, the deputy director of Upshur County’s Office of Emergency Management, Steve Milligan, said.

Samantha Lewis, whose 28-year-old husband, David, was among those trapped, said he worked the mines so that he could be home every night to take care of their three daughters while she worked on a master’s degree in health care administration.

“This was a good way to make a living until we could find something else,” Ms. Lewis, whose father, grandfather, and stepfather also worked in the mines, said. “It’s just a way of life. Unless you’re a coal miner or you have a college degree, you don’t make any money.”

Miners who work in the mine carry individual air purifying systems that would give them up to seven hours of clean air, Tim McGee, who works at the mine and was among those at the church, said. They do not carry oxygen tanks, he said.

Mr. McGee said the miners would have been heading to a production area that is about three miles from the mine’s opening.

“There’s always that hope and chance that they were able to go to part of the mine that still had safe air, and they have all the equipment in order to test that,” the governor of the nation’s No. 2 coal-producing state told CNN.