(Adds confirmation that plant shut, market outlook, stockpiles)
April 23 (Reuters) - An explosion on Wednesday shut a natural gas-processing plant in Wyoming that can churn out about 2 percent of the daily U.S. gas supply, and a nearby town was evacuated though no injuries were reported.
The blast at the Williams Companies Inc plant in Opal, Wyoming, touched off a fire that was still burning several hours later, company spokeswoman Michele Swaner said.
She said all 42 employees of the plant had been accounted for and were not injured. The Lincoln County Sheriff's Department said the fire had been contained to one area of the plant. Shelters were set up for people in the town of 100 people and nearby Highway 30 was closed.
The explosion, at least the second safety incident suffered by Williams Companies in the last few weeks, could affect prices on Thursday when the market starts trading for gas to be delivered on Friday. <W-OPT-IDX>
The Williams plant feeds into the Opal Hub, a crossroads for five pipelines that connect to California, Oregon and Canada and head east across the Rocky Mountains. Gas at the Opal Hub for Thursday delivery rose 6 cents to $4.63 per million British thermal units.
Wyoming and U.S. regulators were not available to comment or say if gas flows at the Hub would be affected. Utilities used a record amount of gas this past winter to meet heating needs during unusual cold snaps that caused volatile prices and left stockpiles at their lowest level since 2003.
A string of accidents involving the country's overburdened pipeline and rail infrastructure has prompted new safety concerns as U.S. output of oil and gas surges during an unprecedented boom.
On March 31, a pipeline within its liquefied natural gas facility in Washington exploded and shrapnel from the blast caused a leak in one of two liquefied natural gas tanks, prompting evacuation orders near the plant outside the rural town of Plymouth.
On April 7, a Williams unit said that a gas gathering pipeline in West Virginia caught fire.
Williams operates two natural gas processing plants in Wyoming which remove liquids and other impurities from natural gas to allow it to be transported in large pipelines.
Gas comes to the processing plants from the Williams gathering system, a network of 3,500 miles (5,600 km) of pipelines which collect gas produced in the region.
The Opal processing plant has capacity of 1.5 Bcf/day. That is about 2 percent of U.S. daily gas supply of some 70 Bcf/d.
Including the Echo Springs processing plant, which was not affected by the explosion, the combined daily capacity of the two plants is more than 2.2 Bcf/d of natural gas and nearly 125,000 barrels per day (bpd) of natural gas liquids.
Wyoming leads the nation in coal production and is also a top gas producer. Wyoming accounted for more than 7 percent of U.S. marketed gas production in 2013, according to the U.S. Energy Information Administration. (Reporting by Dan Whitcomb; Additional reporting by Eileen O'Grady; Writing by Terry Wade; Editing by Sandra Maler)