* Explosion sets surrounding buildings on fire
* Several people treated for smoke inhalation
* Cause of blast so far unclear
Dec 11 (Reuters) - A natural gas pipeline exploded in flames near Charleston, West Virginia, on Tuesday, setting nearby buildings on fire and injuring several people, authorities said.
The blast, on Nisource's Columbia Gas Transmission pipeline, occurred at midday near Sissonville, about 10 miles north of Charleston, they said.
Surrounding homes and buildings caught fire, and several people suffered smoke inhalation, said West Virginia State Police Sergeant Chris Zerkle. They were being treated at local hospitals, he said.
There were no reports of any fatalities so far, he said.
A Nisource spokeswoman, who confirmed that the incident occurred on its line, said the fire had been contained.
The cause of the explosion was as yet unknown and being investigated, she said.
"Right now we have substantial damage done to several residences and buildings," Zerkle said. "They were substantially damaged beyond recognition."
Nearby Interstate 77 also was badly damaged, he said. It was closed to traffic in both directions and would remain so indefinitely, he said.
The fire "basically melted the blacktop completely off it," Zerkle said.
Also, a bridge on the interstate appeared to have shifted from the blaze's extreme heat, he said.
Although the fire was out, firefighters were tackling "hot spots" including residences that were demolished by the blast, Zerkle said.
A nearby nursing home was not hit, said Michael Slater of the Metro Emergency Operations Center in Charleston.
An initial report had said a gas well exploded, Slater said.
It was unclear how much natural gas supply was disrupted, but Nisource said it did not anticipate any impact to customers.
The largely rural Sissonville, in Kanawha County, is roughly 13 square miles and straddles the interstate.