Five workers were missing and first responders were still trying to brainstorm a way to shut in a burning natural gas well after a rig exploded and caught fire in eastern Oklahoma early Monday, local emergency management officials said.

Authorities received a call at 8:45 a.m. CST about the incident, which occurred at a Red Mountain Energy LLC site just west of Quinton, Pittsburg County Sheriff Chris Morris told the news media during a press conference Monday afternoon. Seventeen workers were evacuated, but five still remained unaccounted for, he added.

One worker was treated for minor burns at the site, but refused transport to a hospital. No other injuries were initially reported, emergency management officials said, but medical helicopters were reportedly dispatched to the scene.

The cause of the incident is unclear. Pittsburg County Emergency Management Director Kevin Enloe said the rig belonged to Patterson-UTI Energy Inc. Morris added that fire departments and other emergency management personnel from neighboring communities were called to assist with the incident. Well fire-fighting specialist Boots & Coots International Well Control Inc. reportedly was on the scene to deal with the ongoing gas-fire at the mangled site, a spokesperson at the Oklahoma Corporation Commission (OCC) told NGI’s Shale Daily.

“All they’re doing is sitting back and watching it right now…We’re not trying to put water on it and spread the hazmat, if you will, because there’s going to be lots of contaminants on location,” Enloe said. “They’re not pumping water on it at this time. They’re letting it burn itself out.”

He added that the remote switch that controls the blowout preventer was damaged in the blast. Emergency management officials, Red Mountain and the well control firm were working on a way to the shut-in the well on Monday afternoon.

OCC spokesman Matt Skinner said Red Mountain Energy affiliate Red Mountain Operating LLC is responsible for the site. He said the company was permitted to drill a horizontal natural gas well at the location and added that OCC’s records show the company was still drilling the vertical leg.

According to Patterson’s rig locator system, Rig 219, a large 1500 hp APEX model equipped with a hydraulic walking system was the only one operating in Pittsburg County on Monday. Footage from local news media outlets showed flames consuming the rig and spouting into the air after the blast. “They’re all pretty shook up from what I’ve seen, as expected,” Morris told reporters when asked how the rig crew was handling the incident. “It’s a pretty traumatic thing to go through.”

Enloe said there were enough firefighters on site to deal with any flames escaping the rig and surrounding area. Other than having to deal with a few grass fires and secondary explosions, first responders were keeping their distance.