One person was injured and another went missing after an explosion shut down a Chevron natural gas plant in Pennsylvania on Tuesday. 

Around 6:45 p.m. Tuesday morning, a well exploded at Chevron's Appalachia's Lanco 7H well in Greene County, Pennsylvania, sending black smoke billowing into the air. Emergency crews responded to immediately, but officials fear the flames are so intense it will take days before crews can reasonably combat the fire. One person was taken to the hospital to treat minor injuries, while a search continued late Tuesday for the missing employee. "Chevron's primary concern at this point is to contain the fire and ensure the safety of its employees, contractors and the surrounding community," company spokesman Kent Robertson told Reuters.

The company does not yet know what caused the blast. Bloomberg reports drilling at the site began in March, 2012, and that Chevron has a heavy stake in the area:

Chevron owned the third-largest acreage in the Marcellus shale as of the third quarter, according to data compiled by Bloomberg. Production of natural gas from the Marcellus, helped by hydraulic fracturing and horizontal drilling, was expected to exceed 13 billion cubic feet a day in December, up from less than 2 billion cubic feet in 2010, the Energy Information Administration said.

Helicopter footage taken by a local news crew shows black marks from the initial blast extend beyond the well and a fire still burning late in the day: