Five other homes had extensive external damage, and several people were treated for smoke inhalation, but authorities said there were no fatalities and all residents had been accounted for.
"We've been very fortunate," said Gov. Earl Ray Tomblin, who toured the damage then briefed the media. "They were just lucky enough not to be home."
Most were at work. One man had just left to go hunting, he said.
State Police spokesman Sgt. Michael Baylous said a slight risk of a secondary explosion remained, so people who had initially been told to stay inside nearby homes were later urged to evacuate.
The explosion occurred between Sissonville and Pocatalico just before 1 p.m. in a 20-inch transmission line owned by NiSource Inc., parent of Columbia Gas. The gas flow was shut off, but State Police 1st Sgt. James Lee said there was still pressure on the transmission line.
Kent Carper, president of the Kanawha County Commission, said flames had been shooting 50 to 75 feet into the air before the fire was extinguished.
"It sounded like a Boeing 757. Just a roar," he said. "It was huge. You just couldn't hear anything. It was like a space flight."
Trevor Goins lives about a half-mile from the explosion and was watching television in his apartment when he saw a ripple in his coffee cup and the floor shook.
"I thought possibly (it was) a plane crash," said Goins, who immediately went outside with several neighbors. "It was so loud it sounded like a turbine engine. You almost had to put your hands over your ears."
He got in his car and drove closer, seeing fire that stretched as high as the hilltops.
"The flames were so high, they were so massive," he said. "I could only imagine what had happened."
Carper said the flames spanned about a quarter of a mile and ran through a culvert under the interstate.
"It actually cooked the interstate," he said. "It looks like a tar pit."
Tomblin said a roughly 800-foot section both directions was baked by the heat.
"It turned the asphalt to cinder," he said, after walking across it. "Your feet were hot. It was like walking on a volcano."
Transportation Secretary Paul Mattox said contractors are already working on repairs, and the state hopes to have the highway reopened by Wednesday night. Crews were expected to work through the night to remove the asphalt and grind the roadway down to the original concrete before repaving.
"We're going to do everything we can to get it back," Mattox said.
Guardrails melted, utility poles burned, an ordinarily reflective green interstate sign was burned down to white metal and the blast blew a huge hole in the road, throwing dirt, rocks and debris across the interstate.
"Even the hillside was on fire," Tomblin said. "There are some homes in close proximity that are still smoking."
Tom Miller, training officer at the Sissonville Volunteer Fire Department, marveled at the destruction.
"Four lanes are gone," he said, adding that it was remarkable that no motorists were injured. "We were very lucky – no rush-hour traffic."
Federal and state investigators are now trying to determine the cause.
"It's one of those rare events that happen," the governor said, "and at this time we do not have those answers," he said
NiSource spokesman Mike Banas said the company was still gathering facts.
"Our first priority is the safety of our employees and the community," he said, adding that no impacts on customers are anticipated.
U.S. Sen. Jay Rockefeller, who chairs the Senate Commerce Committee and has made pipeline safety a priority, vowed to get answers.
The West Virginia Democrat said the National Transportation Safety Board is launching a team "imminently" to investigate, he said, as is the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration.
Smith reported from Morgantown.