A significant number of strange UFOs have been floating over the US, according to Navy pilots.

Numerous experienced pilots spotted the mysterious objects, flying at speeds and for lengths of time that would seem impossible with known technology, flying around in US airspace.

The mysterious objects look like huge, white Tic Tacs and fly with no visible engine or exhaust fumes coming out of them. They appear to be able to execute manoeuvre that human pilots would never be expected to pull off: rotating in the air, and accelerating and stopping at possibly fatal speeds.

The latest reports are just the latest in a series of mysterious and unexplained reports of UFOs by US pilots. They have become so prevalent – and so little appears to be understood about where they have come from – that the US Navy has changed its reporting procedures in an attempt to learn more about where they are coming from.

The pilots involved have said they will not speculate on the origin of the aircraft. "We’re here to do a job, with excellence, not make up myths," one told the New York Times, which interviewed five pilots about their previously undiscussed experience.

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But the craft are moving in such strange and apparently impossible ways that no normal explanation has yet been made. Experts say that any alien explanation is unlikely, though they have not yet been able to rule it out, but it is more likely that it is the result of more mundane effects like bugs in the tracking systems and cognitive overload from such intense flights.

The new reports come from pilots who had been flying through 2014 and 2015 over the East Coast of the US.

Pilots first became aware of the craft when it showed up on radar tracking systems, they said, and initially thought it was the result of a secret drone programme. But they became more mysterious when they started seeing them in real life.

One pilot said that he had almost crashed into one of the objects, which was described as looking like "a sphere encasing a cube". Because the pilots were in danger of hitting the objects, they complained that if the craft were part of a secret programme it could be putting their lives at risk.

In one of the sightings, which was captured on video, a pilot said he had nearly crashed into an object that was flying at a shocking speed. In the footage, pilots express wonder at the objects' flight, exclaiming: “Wow, what is that?" and "Look at it fly!”

One of the pilots said that the planes appeared able to stay in the sky far longer than any known aircraft would normally be able to.

“These things would be out there all day,” Ryan Graves, a pilot who has flown with the Navy for more than 10 years and reported his sightings to the US government, told the NYT. “Keeping an aircraft in the air requires a significant amount of energy. With the speeds we observed, 12 hours in the air is 11 hours longer than we’d expect.”

And they were flying in ways that could kill a human crew, seeming to accelerate, stop and turn almost instantly.

"Speed doesn’t kill you,” Lieutenant Graves said. “Stopping does. Or acceleration.”