For more updates on the West Virginia mine story, read the full CNN.com story.
[Updated at 8:39 p.m.] Don Blankenship, the chief executive officer of Massey Energy Co., which oversees the mine, said in a statement that the company is "working diligently on rescue efforts."
"Our prayers go out to the families of the miners," he said. "We want to assure the families of all the miners we are taking every action possible to locate and rescue those still missing."
[Updated at 8:20 p.m.] The death toll has risen to seven people. At least 19 people remain unaccounted for in the blast.
[Updated at 7:59 p.m.] A spokeswoman at Charleston Area Medical Center, which was being prepared to receive injured miners, told CNN that as many as 28 people are unaccounted for, citing emergency dispatchers coordinating response efforts at the mine.
CAMC spokeswoman Elizabeth Pellegrin said the hospital received one person from the mine via a helicopter at 6 p.m. That patient is getting treatment in the hospital's Intensive Care Unit, she said, declining to elaborate on the person's injuries.
[Updated at 7:13 p.m.] Three other deaths have occurred in the Upper Big Branch Mine in the past 12 years, according to federal records. In 1998, a man was killed when a beam he was constructing collapsed; in 2001, a worker died after a rock fell on him; and in 2003, an electrician who was repairing a shuttle car was found dead, according to the Mine Safety and Health Administration.
[Updated at 6:50 p.m.] At least six coal miners are dead, 21 are injured and another 21 are unaccounted for in the explosion, according to Boone County dispatcher Michael Mayhorn.
Raleigh County officials called his office and those of nearby Logan and Kanawha counties to assist in responding to a mine collapse, he said. At least 20 ambulances and three helicopters were dispatched, and the state medical examiner was en route, Mayhorn said.
[Updated at 6:41 p.m.] Jama Jarrett of West Virginia's Office of Miners' Health, Safety and Training talks to CNN's Wolf Blitzer.
[Updated at 6:37 p.m.] West Virginia's state mine director reported that six coal miners were dead and 21 were missing after the explosion in Raleigh County, according to CNN affiliate WCHS.
[Updated at 6:20 p.m.] More than 20 people are unaccounted for, according to Jimmy Gianato, West Virginia's director of homeland security.
The blast occurred in Raleigh County, at Massey Energy Company's Performance Coal Company Upper Big Branch Mine, the company said. Rescue teams and state and federal agencies were responding.
Massey Energy Company, based in Richmond, Virginia, has operations in West Virginia, Kentucky and Virginia. It is the largest coal producer in Central Appalachia, it said in a statement.
[Updated at 6:13 p.m.] CNN affiliate WCHS reports that dozens of miners are believed to be trapped.
[Posted at 6:06 p.m.] An explosion occurred Monday in a mine in Raleigh County, West Virginia, Massey Energy reported.