(CNN) -- Seven miners were dead and 28 others were unaccounted for after an explosion in an underground mine in Raleigh County, West Virginia, the mine's parent company said.
Another 21 miners were injured in the blast at the Upper Big Branch Mine, according to Michael Mayhorn, emergency dispatcher for Boone County, which was called in to assist in the response.
At least 20 ambulances and three helicopters were dispatched from surrounding counties, and the state medical examiner was heading to the scene, Mayhorn said. At least one miner was evacuated by helicopter, according to Mayhorn.
The explosion happened about 4:30 p.m. at Massey Energy's Performance Coal Co. mine in Whitesville, West Virginia, 30 miles south of Charleston, West Virginia, CNN affiliate WCHS reported.
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".
Miners paced outside the mine shaft, trying to help emergency responders treating their injured colleagues, said Shawn Kline, a reporter for CNN affiliate WVVA.
"The look of worry is on just about everyone's faces," Kline said as dozens of fire trucks, ambulances and police cars streamed into and out of the site.
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.
Sen. Jay Rockefeller, D-West Virginia, said in a statement Monday that he is "working with state and federal officials to get as much information as possible and ... doing all I can to help make sure all resources are made available for this rescue effort".
Massey Energy Co., 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.
Three other deaths have happened 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.
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