Double sonic booms heard over secretive military base Area 51 has sparked claims the CIA is hiding alien technology at the top secret site.

Footage has surfaced of two loud thumping sounds as a pair of F-22 fighter jets fly over the secretive base.

Conspiracy theorists claim the sonic booms show the CIA is secretly testing alien technology or hypersonic aircraft.

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A double sonic boom heard over Area 51 has sparked claims the CIA is 'hiding alien proof' at the top secret site. Footage has surfaced of two loud thumping sounds as a pair of F-22 fighter jets fly over the secretive base

AREA 51 Area 51 is a US Air Force Base around 80 miles (130 km) from Las Vegas, and is thought to be used in the development and testing of experimental military aircraft. The US government only admitted the base exists in 2013 after a Freedom of Information request. The facility had been used during World War Two as an aerial gunnery for Army Air Corp pilots. Famous machines developed there include the U-2 spy plane, SR-71 Blackbird, and the F-117A Nighthawk stealth fighter. Many conspiracy theorists claim the base has been used to research an alleged crashed alien spacecraft at Roswell, New Mexico, in 1947. Advertisement

A clip posted to YouTube by UFO Seekers, taken in the Nevada desert near where Area 51 is based, shows the F-22 craft cut across the sky at speeds of up to 1,500 mph (2,400 kph).

As one jet speeds away, leaving a distinctive vapour trail in its wake, two sonic booms are heard.

The loud cracking sounds are caused by shock waves produced when aircraft travel faster than the speed of sound.

Some users reported seeing a burst of flames burst from the plane's engines.

YouTube commentators claimed the flybys were a cover-up for work on extra-terrestrials within the base.

User Good Citizen wrote: 'They have to be testing cloaking ufos. Sonic bombs dont just happen for no reason.'

User Matt Smith commented: 'I think the regular fighter jets, F22's etc, were there as a distraction, to cover for the real testing of experimental hypersonic aircraft.

'The burst of flame you captured is possible evidence of some type of Scram/Ram Jet type technology, maybe the cause of the double sonic boom?'

User 21 Savage wrote: 'Still waiting for the day for NASA and the whole world to officially tell us that extraterrestrial aliens have been living with us this whole time and that they are real.'

Area 51 is a US Air Force Base around 80 miles (130 km) from Las Vegas, and is thought to be used in the development and testing of experimental military aircraft.

The US government only admitted Area 51 exists in 2013 after a Freedom of Information request. Pictured is a warning sign out the base

Conspiracy theorists have claimed the sonic booms indicate the CIA is secretly testing alien or military hypersonic technology. Area 51 is a US Air Force Base around 80 miles (130 km) from Las Vegas

Famous machines developed there include the U-2 spy plane, SR-71 Blackbird, and the F-117A Nighthawk stealth fighter

The US government only admitted the base exists in 2013 after a Freedom of Information request.

The facility had been used during World War Two as an aerial gunnery for Army Air Corp pilots.

Famous machines developed there include the U-2 spy plane, SR-71 Blackbird, and the F-117A Nighthawk stealth fighter.

Many conspiracy theorists claim the base has been used to research an alleged crashed alien spacecraft at Roswell, New Mexico, in 1947. Pictured is an SR-71 blackbird held upside down during testing at Area 51

Images of the base are extremely rare, with any photographers brave enough to travel there kept far back from the perimeter by the base's many armed guards. Area 51 is blanketed by a strict 23 by 25-mile (37 by 40km) no-fly zone for civilian aircraft

Many conspiracy theorists claim the base has been used to research an alleged crashed alien spacecraft at Roswell, New Mexico, in 1947.

Images of the base are extremely rare, with any photographers brave enough to travel there kept far back from the perimeter by the base's many armed guards.

Area 51 is blanketed by a strict 23 by 25-mile (37 by 40km) no-fly zone for civilian aircraft.