People wait to enter Walter Reed National Military Medical Center in Washington, DC, during an emergency drill on November 27, 2018. (Xinhua/AFP PHOTO)

WASHINGTON, Nov. 27 (Xinhua) -- An "all clear" has been given after reports of an active shooter at Walter Reed National Military Medical Center in Bethesda, U.S. state of Maryland, authorities said Tuesday afternoon.

"No active shooter was found" and "personnel may now move freely," tweeted Naval Support Activity Bethesda, which oversees operational support for its major tenants at the base, including Walter Reed.

U.S. Navy tweeted that it was an "ad hoc drill by tenant command."

Local news outlets said earlier that police were responding to reports of an active shooter who was said to have been in the basement of a building at the Maryland base.

The basement was cleared at around 3:00 p.m. local time, according to the base.

U.S. Congressman Dutch Ruppersberger, who serves Maryland's 2nd District, tweeted earlier that he and about 40 other people were safe in a conference room at the medical center and that they had been told "there is an active shooter."

"At no point was there any indication that this was a drill," Ruppersberger said in a tweet later.