MYSTERY WIRE — A close call with a medical helicopter is raising the stakes as authorities investigate a fleet of drones flying night missions over northeastern Colorado.

Ground-based spotting teams and an aircraft equipped to hunt drones will be deployed, according to the Colorado Department of Public Safety.

Media reports indicate additional aircraft might be brought into the search.

ABC News reports that the close call with the Flight for Life helicopter occurred on Tuesday night near Fort Morgan, Colorado.

An aircraft known as a Multi-Mission Aircraft uses heat signatures to track objects, but no drones were detected Monday night when the MMA flew a mission that was nearly five hours long.

A report from Dr. Simeon Hein, author of “Opening Minds: A Journey of extraordinary Encounters, Crop Circles and Resonance,” indicates that drones could have a total value of around $1.5 million. The drones have been described as weighing over 50 pounds, with 6-foot wingspans and the ability to hover in place for 90 minutes.

The drones have been reported throughout northeastern Colorado, across Nebraska and in some parts of Kansas. The drones had flown “grid patterns,” as if they were searching or mapping the area.

Residents in rural northeastern Colorado have been reporting the drones to local law enforcement since Dec. 20.

Speculation has centered on military testing or experiments, but military agencies have denied they are behind the drones.