WASHINGTON – An unmanned Army surveillance blimp broke loose from its ground tether at a military base in Maryland on Wednesday and drifted over central Pennsylvania as two Air Force fighter jets tracked it. The blimp’s long tether snapped power lines, causing outages.

Pentagon officials said the blimp was descending.

The North American Aerospace Defence Command in Colorado said the blimp detached from its station at Aberdeen Proving Ground, Maryland, at about 12:20 p.m., and initially travelled north at an altitude of about 16,000 feet.

State police in Columbia County, Pennsylvania, confirmed they had been getting 911 calls about blimp sightings, but they could not provide additional details.

Witnesses reported seeing the blimp drifting between Jerseytown and Turbotville, a sparsely area north of Harrisburg. Its tether was snapping power lines.

Military Aerostat Detaches from Mooring Press Release pic.twitter.com/x07aWZoy5t — NORAD & USNORTHCOM (@NoradNorthcom) October 28, 2015

The local electric utility, PPL, reported about 20,000 customers without power in the area, although it was unclear how many could be attributed to the blimp. Bloomsburg University cancelled classes, citing a “widespread power outage.”

The blimp is the kind used extensively in the Iraq and Afghanistan wars to provide ground surveillance around U.S. bases and other sensitive sites.

“My understanding is, from having seen these break loose in Afghanistan on a number of occasions, we could get it to descend and then we’ll recover it and put it back up,” Defence Secretary Ash Carter said in a brief exchange with reporters at the Pentagon. “This happens in bad weather.”

Carter did not say what the two F-16 fighters tracking the runaway blimp might be asked to do or whether he considered it a threat to aviation.

The F-16s were launched from the Atlantic City Air National Guard Base in New Jersey, according to the NORAD statement.

FAA officials were working with the military to ensure air traffic safety.

The aircraft is known as a Joint Land Attack Cruise Missile Defence Elevated Netted Sensor System , or JLENS, and can be used as part of a missile defence system.wb

It was not immediately clear how the blimp came loose.