Mass of mystery drones alarm US officials, residents

A rash of unexplained drone sightings in the skies above New Jersey has left locals rattled and sent US officials scrambling for answers.

Breathless local news reports have amplified the anxious sky gazing and wild speculation interspersing blurry, dark clips from social media with irate locals calling for action.

For weeks now, the distinctive blinking lights and whirling rotors of large unmanned aerial vehicles have been spotted across the state west of New York.

But military brass, elected representatives and investigators have been unable to explain the recurring UFO phenomenon.

Sam Lugo, 23, who works in the Club Studio gym in New Jersey's Bergen county, one of the corners of the state that has seen several drone sightings, called the reports "crazy".

"It's pretty concerning they were sighted...without explanation. It can be alarming," he said.

Officials, including the governor, have called on people not to be alarmed, but have not yet offered an explanation for the aerial activity.

The clamour for transparency intensified on Thursday when the four senators for New Jersey and New York called on the FBI, department of transportation and homeland security (DHS) to brief them on how the agencies were working to "identify and address the source of these incursions".