Unmanned flying drone flies across a farm
Colorado resident David Lesh found missing ophthalmologist Guillermo DeVenecia with a helicopter droneGetty

An amateur drone operator used his flying helicopter drone to locate a missing elderly man in 20 minutes, after a three-day police search-and-rescue effort that included hundreds of volunteers, search dogs and a helicopter failed to find him.

According to Wisconsin local TV station NBC 15, Colorado resident David Lesh was visiting his girlfriend's family in Fitchburg, Wisconsin, when he heard a manhunt was going on to find missing ophthalmologist Guillermo DeVenecia, 82.

Police and hundreds of volunteers had been searching for three days, so Lesh decided to join the effort using his drone, which he had brought with him.

"I never thought that I would be using it to find somebody," said Lesh, who bought the flying drone so he could film aerial ski and snowboarding footage.

"We weren't really sure what we would find or what kind of shape he would be in if we did find him... I don't think any of us expected to find him."

Lesh flew his drone over a 200-acre field, reviewing footage from its camera to see if he could spot DeVenecia. It would have taken volunteers hours to search the same area by foot.

Within 20 minutes, Lesh and his girlfriend, Katie Gorman, had flown the plane over most of the field and when Lesh directed the drone to the final corner of the field, he found DeVenecia, shoeless and stumbling around.

"To be honest, when David was flying the drone over the bean fields, we thought we were looking for a body," said Katie's father, Gary Gorman.

The Gormans and Lesh carried DeVenecia to their car and took him back to the police command centre.

DeVenecia told his rescuers he thought he had been out for a short walk and did not understand why people had been looking for him.

The US Federal Aviation Administration (FAA) has not been keen on flying drones from the get go and is only now starting to consider them for commercial purposes.

Consideration is under way into new rules about what drone enthusiasts are allowed to do with unmanned flying drones and there have been lots of recent media reports about drones being used to spy on unsuspecting citizens or to survey private property for nefarious purposes.