A gas line exploded Monday in rural Kentucky, burning four houses and injuring eight people, including an off-duty state trooper who helped others escape, officials said.

Rick Conn, the off-duty trooper, lived in the neighborhood and suffered third-degree burns helping people escape, officials said. He was airlifted to St. Mary's Hospital in Huntington, W.Va., where he was in fair condition.

There were no immediate reports on what caused the explosion, state Emergency Management Agency spokeswoman Stacy Floden said.

Four people were being evaluated at hospitals in the area, and three others were treated and released.

The gas line is owned by Kentucky-West Virginia Gas (search) and maintained by Mark West Hydrocarbon Inc. (search)

"We're trying to find out all the facts of the situation," said Cory Bromley, Mark West's general counsel.

Ivel is in eastern Kentucky, not far from the Virginia and West Virginia state lines.