The explosion happened late on Monday afternoon, rocking the remote Upper Big Branch mine in the town of Montcoal, some 50km south of Charleston.
A massive rescue operation was launched, with local and volunteer firefighters rushing to the scene, along with a fleet of ambulances.
Mine safety workers tried to contact missing miners underground, but the search was halted early on Tuesday, with four men still unaccounted for.
Two other workers were injured in the blast, and are being treated in hospital.
The mine is reported to have had a history of safety problems.
Prayers for miners' families "Massey Energy Company is confirming twenty-five fatalities at its Upper Big Branch Mine, resulting from a tragic explosion," the company said in a statement.
"Our prayers go out to the families of the miners," said Don Blankenship, chairman and chief executive of Performance Coal Company, a subsidiary of Massey Energy.
US President Barack Obama telephoned West Virginia governor Joe Manchin to offer his "deepest condolences to the those who lost loved ones earlier today in the tragic incident".
"This is devastating news and our hearts and prayers go out to the families of the miners who have died," the governor said in a statement.
"We are offering everything we can to assist those families at this time."
Manchin asked everyone to "pray for the miners, their families and our rescue teams".
Worst disaster in 26 years
In Washington, West Virginia senator Jay Rockefeller said he and his wife were "heartbroken" at the news.
"We are sending all of our prayers and thoughts to the brave miners and their families," Senator Rockefeller said.
Monday's disaster is the worst in the US since 1984, when 27 people were killed in a fire at Emery Mining Corp's mine in Orangeville, Utah.
In January 2006, 12 West Virginia coal miners died in the Sago coal mine, owned by the International Coal Group, after they were trapped by an explosion 80 metres underground. One miner survived.
The worst-ever US mining disaster was in 1907 in Monongah, West Virginia, where an explosion killed 362 workers.
