The skies over one New Jersey county have baffled residents for weeks, with mysterious drones repeatedly flying overhead.

The drones have been appearing frequently over the nighttime sky at Morris County late at night, with locals speculating on social media that it could be anything from surveillance to UFOs. Residents are growing concerned about their origin and so is the FBI, according to a report from the Morristown Daily Record.

“We are working with our state and local partners on the reported drone activity,” officials with the FBI’s Newark Field Office said to the local newspaper.

The drones were first spotted in mid-November, and area resident Mike Walsh told NBC4 New York that he now sees them all the time.

“We’ve been seeing them every night, except Thanksgiving. I guess they took the night off,” Mr. Walsh said, describing how he had heard what sounded like a helicopter from inside his house the first time he spotted a drone flying overnight.

“I’d really like to see one land and report it, but they’re up for a long time. I don’t know where they’re taking off from, where they’re landing,” he added.

As more sightings were spotted, speculation increased.

“People think they were UFOs or being spied on,” Erica Campbell said to NBC4 New York.

Christian Velasquez also spotted a drone one night recently.

“It was flying right over this church, continued past the train station. It had three blinking lights,” he recalled to the local news station. “It’s weird. There’s multiple being spotted at the same time all around Morris County. It’s definitely concerning.”

As more reports have come in, local police officials have issued Nixle alerts to residents.

“We are aware of drone activity in the area,” Morristown Police advised through the text messaging system. “If you observe a drone, please contact the Morristown Police Department. In the event that a drone crashes or lands, do not approach or handle it.”

In an advisory, Morris County officials said there was “no known threat to public safety” and attempted to quell rumors on social media.

“We encourage the public to be mindful that what they read online may not be accurate,” reads a statement from county officials.

Sightings were also spotted in areas considered no-fly zones, including near the Morristown Municipal Airport.

Drones have also been seen hovering in the skies of neighboring Warren County, according to the President of Warren County Community College, William Austin, who also teaches drone piloting.

“It raises concerns among any citizen, people who manage airports or man aircraft in the sky,” he said to the Daily Record, adding that it won’t take long to find the pilot, or pilots, manning the mystery drones since most contain a GPS identification chip.

“It’s just a matter of time before someone figures out who it is. It’s like flying with LoJack.”