Five people are missing after an explosion at an Oklahoma drilling rig Monday morning, according to news reports.

The explosion happened shortly before 9 a.m. Central time in northeast Pittsburg County, Sheriff Chris Morris said at a news conference Monday afternoon. Twenty-two employees were drilling a gas well at the site when the explosion happened; five remain unaccounted for, while the others were able to get out safely, Morris said.

One had minor burn injuries and refused to be taken to the hospital, officials said.

Images and videos taken by local media show several fires burning as thick black smoke blanketed the facility. The explosion, which happened near the town of Quinton, about 140 miles southeast of Oklahoma City, sent black smoke to nearby farmlands.

The cause of the explosion is not yet known. The Occupational Safety and Health Administration, or OSHA, is investigating the incident and interviewing employees.

Those missing are employees of Houston-based Patterson-UTI Energy Inc., which owns the drilling rig. The company confirmed in a statement that some of its employees were reported missing after the explosion.

"Our top priority is the safety of our employees and any others who may be affected," the company said. "We're activated our emergency response systems and are fully cooperating with first responders and authorities on the scene."

County Commissioner Charlie Rogers said the missing employees have been identified, but their names will not be released while their employer contacts family members.

Rogers said the gas well is operated by another company, Oklahoma City-based Red Mountain Operating. A call to that company was not immediately returned.

Fires were still burning by Monday afternoon, though they're no longer spreading, Kevin Enloe, Pittsburg County's emergency management director, told reporters. Officials plan to let the fire run its course instead of placing fire crews close to hazardous materials, he said.

"The fire is pretty much containing itself right now," Enloe said. "There's some fire that is jumping off location because of the flame size. It's getting some gas fires started . . . all we're doing is combating any fire that leaves the location."

The sheriff's office also said a nitrous truck will be used to help suppress the fire, the McAlester News-Capital reported.