CLARKSVILLE, Tenn. (WKRN) — Multiple agencies in Montgomery County spent hours searching for the source of an “unknown phenomena” that involved reports of a loud explosion and the ground shaking.

Clarksville police said the 911 Dispatch Center received several calls around 9:50 p.m. Saturday about a “loud explosion” being heard. Several of the callers reported they felt the ground shake, as well.

The calls came from all over Montgomery County, but no damage had been reported, according to law enforcement.

Police said officers searched for hours alongside the city’s fire department, the Montgomery County Sheriff’s Office and Emergency Medical Service, but could not find the source.

The United States Geological Survey did not register an earthquake in the area.

Law enforcement agencies added that Fort Campbell is on a four-day weekend due to Labor Day, so it did not appear to be training or an exercise.

Clarksville police described the incident as “some sort of unknown phenomena.”