Large drones have been spotted flying over New Jersey and New York City in recent weeks - but no one knows who's operating them.

The drones are reportedly six feet in diameter and have been seen flying at night, sometimes with their lights off, causing concern among residents and officials.

They were first spotted last month near the Picatinny Arsenal, a US military research and manufacturing facility, and over president-elect Donald Trump's New Jersey golf course.

There have been dozens of night flights since and sightings have increased in recent days, though officials say some of the objects seen may have been planes rather than drones.

The FBI is investigating and has asked residents to share any videos, photos or other information they may have.

The drones have predominantly been seen in New Jersey, with some also being spotted in New York City and parts of Pennsylvania, including over Philadelphia.

Despite national interest, authorities have stressed that the drones don't appear to be a public safety concern.

After being briefed by the Department of Homeland Security (DHS) on Wednesday, New Jersey assemblywoman Dawn Fantasia said she was told the devices did not appear to be being flown by hobbyists, mainly because they are much larger than those typically used by casual flyers.

Republican assemblyman Erik Peterson, who attended the DHS briefing on Wednesday, said they seemed to have "no clue" who was behind the flying objects.

Two Republican Jersey Shore-area congressmen - Representatives Chris Smith and Jeff Van Drew - have called on the military to shoot down the drones, with the latter claiming on Fox News that they are coming from an "Iranian mothership".

But Pentagon spokesperson Sabrina Singh told reporters on Wednesday that "our initial assessment here is that these are not drones or activities coming from a foreign entity or adversary".

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Drones are legal in New Jersey for recreational and commercial use, but they are subject to local and Federal Aviation Administration (FAA) regulations and flight restrictions, and operators must be FAA-certified.

Many local politicians have called for more restrictions on who is entitled to fly the unmanned devices, with some proposing a temporary ban on drone flights in the state.

James Edwards, a resident of Succasunna, New Jersey, told the Associated Press news agency he has seen a few drones flying over his neighbourhood since last month.

"It raises concern mainly because there's so much that's unknown," he said. "There are lots of people spouting off about various conspiracies that they believe are in play here, but that only adds fuel to the fire unnecessarily. We need to wait and see what is really happening here, not let fear of the unknown overtake us."

New Jersey's governor Phil Murphy said earlier this week they were taking the issue "deadly seriously", adding: "I don't blame people for being frustrated."

(c) Sky News 2024: Mystery drones spotted over New Jersey - and authorities have 'no clue' who is flying them