McLEAN, Va. (AP) — An unconfirmed report of an armed person at the Northern Virginia office building that houses USA Today prompted an evacuation and massive police response Wednesday that found no immediate signs of violence.

Fairfax County Police Chief Edwin Roessler said at a news conference that his department got a 911 call around noon from the building saying an armed "former employee" had been seen there.

Roessler said it was not clear yet whether that report was true. A floor-by-floor search of the 11-story building was underway Wednesday afternoon and expected to last for hours, but Roessler said so far there had been no evidence of violence.

"I pray they are not in the building, and that this will end safely," he said.

USA Today reported that alarms sounded and police squad cars converged on the scene in McLean, Virginia, as employees waited outside. Law enforcement officers with rifles and body armor patrolled the area and a helicopter hovered overhead.

Taylor Rosa, an accountant for USA Today's owner, Gannett, said he was in his office when co-workers told him there were police with body armor on the campus. But he and others went back to work. He said his initial guess was that some sort of VIP was visiting the headquarters and had police protection. About five minutes later, they were told to evacuate.

"There were some people that definitely had panic in their faces" as they evacuated, Rosa said.

"Mostly we were just a little confused," he said.

Rosa said he had gotten notice from his human resources department that it may be two to four hours before employees could re-enter the building, a glass structure tucked in Tysons Corner in a row of other corporate campuses.

Photos showed flags there flying at half-staff. The incident came as the nation reels from its latest mass shootings — at a Walmart store in El Paso, Texas, and an entertainment district in Dayton, Ohio. A combined 31 people were killed and dozens wounded in less than 24 hours in those two weekend attacks.

Roessler said he couldn't say for sure whether the person reported to be in the building was a Gannett employee. The building also houses other tenants.

Police were searching for the "person of interest," he said.

The incident came just two days after GateHouse Media, a fast-growing chain backed by an investment firm, announced it was buying Gannett in a $1.4 billion merger of two of the largest U.S. newspaper companies.

The companies said they were committed to journalistic excellence while also cutting costs by $300 million annually. The combined company would have more than 260 daily papers in the U.S. along with more than 300 weeklies.