An explosion Thursday at a small airport's natural gas well injured five people.

A vehicle apparently exploded as a crew was trying to activate the new well at Rostraver Airport, said Dwayne Pickels, administrative assistant with the Westmoreland County Airport Authority. The cause of the explosion was unclear.

The two most seriously injured people were flown by helicopter to a hospital in Pittsburgh, 20 miles north of the airport.

The well is owned by Clarion-based Kriebel Minerals. The five injured employees worked for Kriebel's subcontractor, Halliburton Co., the Houston-based oilfield-services company.