At least 12 coal miners are dead and 10 others are missing deep underground after an explosion in a West Virginia mine on Monday.

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Emergency workers survey the scene of a coal mine explosion that left at least 12 miners dead and 10 others missing in West Virginia on Monday. ((Jon C. Hancock/Associated Press))

A mine safety administrator revised the toll late Monday night. Earlier reports had put the figure at seven dead, with two injured and 19 missing.

State mine director Ron Wooten said the explosion occurred at about 3 p.m. ET at the Upper Big Branch Mine-South in Raleigh County, about 50 kilometres south of Charleston.

Emergency crews were dispatched to the mine, which is near the town of Montcoal. The mine is operated by Massey Energy subsidiary Performance Coal Co.

Wooten said Massey Energy reported the explosion but did not provide details. He said he had not spoken yet with anyone at the scene. 

"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.

He said the names would not be released until next of kin were notified.

One injured miner was in intensive care at Charleston Area Medical Center, spokeswoman Elizabeth Pellegrin said.

"We are preparing for other patients," she said.

The mine, which can't be seen from the road, is a sprawling facility with 19 openings and ceilings well over two metres high.

A mine safety official said seven of the miners who were killed were on their way out of the mine in a vehicle when an explosion occurred.

Kevin Stricklin, an administrator with the Mine Safety and Health Administration, said two other men on the vehicle were hurt. Stricklin said there are 19 others unaccounted for, including two crews of nine workers and a fire boss who had been working alone.

The explosion destroyed all communication lines inside the mine.

Stricklin said there are two rescue chambers near the blast site that are stocked with food, water and enough air for the trapped miners to survive for four days.

Stricklin said officials don't believe there was a roof collapse, but they don't yet know what caused the explosion.

According to the Mine Safety and Health Administration, the mine has about 200 employees, most of whom work underground. Not all would have been working the same shift.

With files from The Associated Press