A MYSTERIOUS “fireball” spotted falling to Earth in the US has sparked an official investigation, after national monitors said no meteor had been detected in the area.

A bizarre “fireball” spotted crashing down into a small US town has left leading scientists baffled. Police deputies in Polk County, Oregon, have admitted they have “no idea” what the object that was witnessed on Thursday afternoon is. The US Air Force and Federal Aviation Administration have also been involved in the mystery.

The fiery trail was reported by a local Salem resident around 4:50 pm local time on Thursday.

The initial witness feared that the object was a potential plane crash.

However, that theory was ruled out by the US Air Force, according to Lt. Dustin Newman from the Polk County Sheriff’s Office (PCSO).

Despite a widespread search, the location of the mysterious crash remains undetermined, according to the PCSO.

A bizarre “fireball” spotted crashing down into a small US town has left leading scientists baffled

The PCSO posted images of the sighting on its official Facebook page.

They wrote on Facebook: “PCSO is currently investigating a large fireball falling to the earth in the southwest area of Polk County.

“The fireball was reported as a plane crash and PCSO is working to locate a possible landing location and exactly what the fireball is.

“PCSO will utilize aircraft during daylight hours Friday in an attempt to cover the rough terrain in the area and wrap up the search.”

“PCSO has utilized all available aviation tracking systems and no planes have been lost.”

Several national and local authorities, including the US Forest Service, a Life Flight Network helicopter and a local timber company, are working together to determine the origin of the fireball

The mystery deepened when the American Meteor Society and NASA’s Center for Near Earth Object Studies refused to say whether meteors had been picked up in the area.

The police have since opened up an investigation into the sighting, amid a frenzy of speculation about its true origins.

Richard Romano, who captured photographs of the sighting, ruled out a meteor.

He said: “I’ve seen meteors before, and they’re bright white and in five seconds they’re gone. That one lasted way too long.”

Several online viewers speculated on theories including secret military tests, aliens, and meteors.

One resident said: “Could be linked to the secret military stuff that’s been going on around the old town of Valsetz Oregon.”

Elizabeth Yon commented: “It looks like space junk, I’ve seen it before usually a big ball of fire with a purple tail.”