WASHINGTON (AFP) – An explosion ripped through a coal mine in West Virginia, killing 25 workers and leaving four unaccounted for in one of the worst US mining disasters in recent years, officials said.

The blast occurred towards the end of the afternoon at the Upper Big Branch mine run by Performance Coal Company, a subsidiary of Massey Energy, in the town of Mountcoal located some 30 miles (50 kilometers) south of Charleston.

"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. We want to assure the families of all the miners we are taking every action possible to locate and rescue those still missing," the company's chairman and chief executive, Don Blankenship, said.

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."

Obama told Manchin "that the federal government stands ready to offer whatever assistance is needed in this rescue effort," a White House statement said.

A massive rescue operation was launched after the blast as local and volunteer firefighters rushed to the scene along with a fleet of ambulances and mine safety workers tried to contact missing miners underground.

Details about the rescue operation were sketchy, in part because mobile phone services are intermittent at best in the mountainous area of the mostly rural state.

Manchin, who rushed home from a vacation upon learning the news, said Obama had promised "every asset available" to help in the rescue effort.

"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."

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.

"I am working with state and federal officials to get as much information as possible and I am doing all I can to help make sure all resources are made available for this rescue effort."

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 more than 40 hours 80 meters (260 feet) underground. One miner survived.

The worst-ever US mining disaster was in 1907 in Monongah, West Virginia, where an explosion killed 362 workers.

According to official figures, annual fatalities from mining accidents have totaled less than 20 in West Virginia since 1983, except for 1991 when there were 22 and 2006 when there were 25.