The rogue military blimp that broke its tether lines north of Washington is now on the ground.

But on its way down it bumped into a school and hit power lines ... around 20 people have lost electricity.

Two US Air Force F-16s were scrambled to track the blimp, which was full of top secret equipment.

The massive US surveillance blimp broke loose from its mooring in Maryland and is floating toward Pennsylvania with two US fighter jets following it.

The so-called JLENS aerostat, which is nearly the length of a football field, detached from its mooring in Aberdeen Proving Grounds at around 12.20pm local time, the North American Aerospace Defense Command (NORAD) said in a statement on Wednesday.

Two F-16 fighters were monitoring the helium-filled blimp as it floated northeast of Washington at an altitude of about 4875 metres.