US fighter jets scrambled after giant blimp breaks free and starts drifting over Pennsylvania

The 1.3-mile-long chain the blimp is dragging behind it has caused power outages

US military fighter jets were scrambled to track a giant unmanned blimp that tore loose from its tethers and began drifting across the sky.

According to a statement from the North American Aerospace Defence Command (NORAD), the blimp detached from its anchor station in Maryland on Tuesday afternoon.

Shortly after it took to the skies, two F-16 jets took off from a National Guard base in New Jersey to monitor the 75-metre long blimp.

Local news reported it was drifting north towards Pennsylvania at an altitude of around 16,000 feet, slightly less than half the cruising altitude of a commercial airliner.

The blimp, a JLENS radar-equipped aircraft, was part of a $2.7 billion Pentagon programme aimed at providing an early warning system in case of an aerial attack on the US.

However, the programme has reportedly proved unsuccessful, with the blimp turning out to be expensive and ineffectual at its intended task.

Judging by eyewitness reports, the balloon appears to have descended a little, with photos showing it passing quite low overhead.

The blimp is also dragging its 1.3 mile tether chain behind it, which began trailing across the ground and causing damage after it descended.

The chain hit power cables as it dragged along, causing widespread powercuts in its wake - all classes at Pennsylvania's Bloomsberg University were cancelled due to power outages caused by the blimp.

It is not immediately clear how the blimp came loose in the first place, but and officials and police are working to ensure the safety of air traffic and those on the ground.