The US military is scrambling to recover an expensive spy blimp that broke loose from its moorings and is threatening air traffic north of Baltimore, Maryland. Fighter jets are shadowing the helium-filled balloon as it drifts over Pennsylvania.

Pentagon spy blimp breaks free UFO over US? No, merely a lost Pentagon surveillance blimp Posted by RT Play on Thursday, October 29, 2015

Known as an “aerostat,” the floating surveillance platform has been moored at the Aberdeen Proving Ground, northeast of Baltimore, since 2014. It broke loose around 12:20 local time Wednesday.

I cost how much and no one even put a tracking device on me? https://t.co/TbbUhhY5TC — AberdeenAerostat (@AberdeenBlimp) October 28, 2015

According to the US Army’s North American Aerospace Defense Command (NORAD), the runaway blimp was first reported at an altitude of about 16,000 feet (4.8 km). It is trailing 6,700 feet (2 km) of cable below, posing a navigational hazard to aircraft.

A viewer just sent us this photo from Bloomsburg. We are getting numerous reports of sightings in that area. #Blimppic.twitter.com/eG3xctQIEn — Jon Meyer (@JonMeyerWNEP) October 28, 2015

Around 3 p.m. authorities in central Pennsylvania reported fires on the ground as the tether tore up power lines. Some 21,000 residents were without power.

Untethered JLENS #blimp cable is dragging the ground in Bloomsburg and causing massive power outages, Columbia Co DPS Director says. — Dianne Gallagher (@DianneG) October 28, 2015

Local media initially reported that the errant airship landed in Columbia County, Pennsylvania, somewhere between Jerseytown and Millville, around 65 miles west of Scranton.

BREAKING PHOTO: Out-of-control blimp near Bloomsburg, Pennsylvania. pic.twitter.com/M8nSY1vF4n — Breaking News (@NewsOnTheMin) October 28, 2015

Eyewitnesses on the ground, however, said the blimp was still airborne, slowing down as the dragging tether pulled it steadily lower.

NORAD said the "partially deflated" blimp made landfall just after 4 p.m. near Williamsport, Pennsylvania.

Here is the #blimp well part of it...in a tree near Muncy @WNEPpic.twitter.com/epkaSuFsxj — Nikki Krize (@NikkiKrize) October 28, 2015

The 240-foot (74-meter) blimp is part of a program by the weapons manufacturer Raytheon named JLENS, which stands for “Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System.” The airborne radar has the ambitious objective of giving early warnings of low-flying missiles and planes.

I should know better by now, but even I still have trouble believing that "runaway surveillance blimp" is actually a thing. — Edward Snowden (@Snowden) October 28, 2015

The 17-year program has cost the Pentagon around $2.7 billion, according to a recent feature in the Los Angeles Times. Raytheon lobbied hard for its survival after the Army tried to cancel it in 2010, leading defense commentators to dub JLENS a "zombie" program: costly, ineffectual and seemingly impossible to kill.

Military may need to shoot down lost blimp. Perfect moment to prove F35 could win a dogfight? https://t.co/vqBGZuTkGr — Peter W. Singer (@peterwsinger) October 28, 2015

JLENS failed spectacularly on April 15 this year, when a postal worker from Florida flew unchallenged through a restricted area around Washington DC in a gyrocopter, landing in front of the US Capitol.

1.4 billion dollar Blimp Missing -- Call DOD if seen. All white, 240ft long, loaded with cool military stuff.... https://t.co/iZZN5Gv5xx — Aviation Digest (@Aviationdigest) October 28, 2015

Authorities in Maryland and Pennsylvania have issued statements that they are tracking the blimp, warning the population to call 911 and not to attempt to engage the runaway sensor platform on their own.

While two F-16 fighters have been scrambled to follow the renegade aerostat, the military hopes to recover the multi-million dollar sensor technology aboard the JLENS rather than shoot it down.