An "all clear" has been issued by federal officials after the D.C. Navy Yard went on lockdown after reports of an active shooter. 

An employee inside the building said alarms were sounding and workers were being told to shelter in place.

A massive police response unfolded, apparently in response to a 911 call about a shooting. 

AP reports now that there has been no evidence of a shooting taking place and no weapons have been found. No arrests were made.

In 2013, a gunman killed 12 people at the complex before he was shot by police. That gunman, Aaron Alexis, was a military contractor and was able to gain access with his ID card.

The Navy Yard, in southeast Washington, is the country's oldest naval installation.

UPDATE, 8:55a ET: 

UPDATE, 9:05a ET: The U.S. Navy said that the lockdown remains in place at the Navy Yard. The D.C. fire department has not confirmed that there were shots fired or that anyone was hurt.

UPDATE, 9:35a ET: Police are interviewing the person who made the original 911 call to report a possible shooter on the premises. It appears that the caller was at the Navy Yard during the 2013 mass shooting,

Stay tuned to Fox News Channel for continuing updates.