Montcoal, W.Va. ? An explosion rocked a remote coal mine with a history of safety problems, killing 12 workers and trapping at least 10 others thousands of feet underground in the worst U.S. mine disaster since 2006.

Rescuers were making their way early today 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 p.m. Monday, said Kevin Stricklin, an administrator for the federal Mine Safety and Health Administration.

“It’s important for us to try to get to the survivors as quickly as possible,” Stricklin said.

He said officials hoped the miners 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.

At the Marsh Fork Worship Center in nearby Eunice, the church doors stood open and a big sign outside read “Pray for Our Miners.”

“You just feel helpless,” said Toby Hilderbrand, who was waiting for word about his wife’s uncle, Ricky Workman, 51, of Coalcord, who was among the miners that had not been accounted for. “There’s nothing you can do but pray, but at times like this the community really comes together.”

Though the cause of the blast was not known, the operation about 30 miles south of Charleston has a history of violations for not properly ventilating highly combustible methane gas, safety officials said.

Miners were leaving on a vehicle that takes them in and out of the mine’s long shaft when a crew ahead of them felt a blast of air and went back to investigate, Stricklin said.

They found nine workers, seven of whom were dead. Two others were injured. Early today, Stricklin raised the death toll to 12.

Officials do not believe that the roof collapsed, but two other crews and a safety inspector who had been working alone were believed trapped about a mile and a half underground.

There was some confusion about how many miners were still unaccounted for. Stricklin, an administrator for Coal Mine Safety and Health, said 10 miners were trapped. MSHA director Joe Main said in an interview with The Associated Press that there could be more and officials were trying to sort it out. In a press release, Labor Secretary Hilda Solis said there were 17 miners still missing.

Distraught family members were briefed and taken to a Massey building off-limits to the media.

“We want to assure the families of all the miners we are taking every action possible to locate and rescue those still missing,” said Massey CEO Don Blankenship, who confirmed the number of dead and missing in a statement.

Massey Energy, a publicly traded company based in Richmond, Va., has 2.2 billion tons of coal reserves in southern West Virginia, eastern Kentucky, southwest Virginia and Tennessee, according to the company’s Web site. It ranks among the nation’s top five coal producers and is among the industry’s most profitable. It has a spotty safety record.

In the past year, federal inspectors have fined the company more than $382,000 for repeated serious violations involving its ventilation plan and equipment at Upper Big Branch, which is run by subsidiary Performance Coal Co. The violations also cover failing to follow the plan, allowing combustible coal dust to pile up, and having improper firefighting equipment.

The mine has had three other fatalities in the last dozen years. Monday’s blast was the worst U.S. mine disaster since the Sago explosion, also in West Virginia, which also killed 12.