No injuries were reported at the U.S. Navy Yard in Washington on Thursday, a spokesman for the Washington D.C. Fire Department said, after the facility was placed on lockdown following reports of a possible shooter.

The Navy Yard was given the all-clear around 10 a.m.

A shooter was not found as police swarmed the Navy Yard, according to a local CBS radio station, amid heightened security concerns ahead of the U.S. July Fourth holiday weekend.

The Navy Yard is a mile south of the U.S. Capitol and three miles from the White House.

There were no injuries or victims, the fire department spokesman said.

A caller told authorities that shots were heard in Building 197, according to multiple reports, the same one that was the scene of the 2013 killings by Aaron Alexis, a former sailor who was working for a government technology contractor at the Navy Yard.

Lieutenant Commander Scott Williams, 39, a guided missile engineer at the Navy Yard, was in the building on Thursday and the day of the 2013 shooting.

He told Reuters that police came to his office at about 7:30 a.m. and escorted him and colleagues out.

"It was pretty much a mirror image of what happened in 2013," he said. "Here we go again."

Williams said security had been tightened after the 2013 incident with more ID checks and random bag searches.

Live television showed a massive police presence in the area, and more than eight blocks of nearby roads were shut down as authorities responded to the scene, the Metropolitan Police Department said.

The Department of Homeland Security and the Federal Bureau of Investigation had issued an alert calling for local authorities and the public to remain vigilant for possible threats during the holiday weekend.

The Pentagon ordered new security measures be put in place after the 2013 shooting. Alexis, 34, had opened fire on Sept. 16, 2013, killing 12 people. He was shot to death after an hour-long exchange with police.

Alexis had reported hearing voices and being unable to sleep in the weeks leading up to the rampage.

The Navy Yard, on the Anacostia River, was established in 1799 as a shipbuilding site and a base for defending the city. The complex houses the Naval Sea Systems Command.