Drones of unknown origin continue to fly over Colorado and are covering more ground, as sightings in Nebraska are beginning to occur.

The mysterious fleet of large drones that have been scoping out rural northern Colorado has increased over the last week.

The number of sightings of drones has increased, as has the number of drones themselves. These unexplained drones have begun to cover a wider swath of area and have been seen in or near Nebraska, as well as in Colorado. Six counties have reports of drone sightings across the two states and authorities still have no clue who is behind them or what the purpose of the drones is. First reported in Yuma and Philips counties, the drone sightings have now been officially reported in Lincoln, Washington, and Sedgwick Counties in Colorado.

Rumors of sightings in Nebraska’s Deuel County have deepened the mystery. Though no official reports have been filed in Deuel County, as of this writing, Sheriff Scott Decoste reports that a deputy saw what appeared to be a fleet of drones flying on the Colorado-Nebraska border, and informed Sedgwick County officials of the incident.

The drone fleet continues to engage in a flying pattern that authorities call a grid search. Phillips County Sheriff Thomas Elliot describes the drones as flying one square then another. They appear each night between 7 and 10 p.m. and hover about 300 feet in the air. The drones fly in groups of six to 10, and no one has been able to catch one, nor have any been reported being seen on the ground.

There haven't been any clues on where these drones came from, or where they head off to each night after their flights. The U.S. Air Force, U.S. Army, the Federal Aviation Administration (FAA), and the Drug Enforcement Administration have all confirmed the drones are not theirs, nor do they have information on who is controlling them.

There are plenty of theories starting to grow, from quite plausible explanations—such as mapping for oil and gas production, solar or wind farm prospecting—to the more speculative spy drones with infrared tracking, drug running drones, and other more nefarious types of ideas.

Though the drones are not flying illegally, it is against the FAA regulations to fly drones that late at night without a waiver being filed. So far, no one has been able to find a waiver filed for these drones. Local authorities and drone experts say they appear to be searching or mapping out the area, often done for crop examination or land mapping purposes. Although the drone fleet’s behavior is not malicious, the nighttime flying is quite mysterious, and the lack of information about why they are out there is adding to the unease surrounding the whole thing. Flying only at night lends to the local’s impression that this is an operation that is intended to be kept mysterious.

Some residents have spoken out online and on social media about throwing rocks at or even shooting down the drones, however, that approach has been advised against by the authorities. The drones are flammable and could possibly explode and hurt or damage people and property; additionally, a drone is considered an aircraft and it is illegal to shoot them down.

This mystery has everyone stumped, and the anxiety over the purpose and intent of whoever is behind these drones is expanding, as is the uneasiness.

What do you think? Have you heard any theories or information about these unmanned crafts that seem to be slowly searching for something under the cover of darkness? We want to hear from you! Share your thoughts and theories in the comments.