There was no immediate word on the cause of the explosion.
The blast was reported at about 2 p.m. and the fire continued to burn Thursday. There's no estimate of when residents will be allowed to go home because it's not known how long it will take for all the gas in the plant to burn off, Lincoln County spokesman Stephen Malik said.
"It burned so hot you can't fight this thing," Malik said of the fire.
The explosion occurred in a cryogenic processing tower, which chills unrefined natural gas to remove impurities.
The fire was confined to the facility, and no structures in the town were affected, county officials said.
All employees at the gas processing plant were accounted for, said Tom Droege, a spokesman for Williams Partners LP of Tulsa, Okla., which operates the plant.
Williams was paying to lodge Opal residents at motels in Little America, about 25 miles east, and in Kemmerer, about 15 miles west.
"We want to make sure everybody's taken care of and they're put up for the night if they're not able to go back to their houses," Williams spokeswoman Michele Swaner said.
The Opal plant removes carbon dioxide and other impurities from natural gas that comes from gas fields in the region. It can gather up to 1.5 billion cubic feet of gas a day, and it sends the refined product into pipelines that go to urban centers to the east, west and south. Lately, the plant has been handling about 1 billion cubic feet of natural gas a day, Williams said.
Williams has temporarily suspended collecting gas from surrounding areas and is looking for ways to resume production.
Regional pipelines converge at a major national hub in Opal, and it's the principal spot where prices are set for natural gas produced from the large gas fields in western Wyoming and the San Juan Basin in Utah. Government officials and industry insiders closely watch Opal hub prices to monitor trends in regional gas supply and demand.
Williams operates the Northwest Pipeline, which runs through Opal on its way to the Pacific Northwest.
Renny MacKay, spokesman for Gov. Matt Mead, said investigators would look into the cause of the explosion once the site was secured.