Washington, Nov 28 (IANS): An "all clear" has been given after reports of an active shooter at Walter Reed National Military Medical Centre in Bethesda, Maryland, authorities said Tuesday afternoon.

"No active shooter was found" and "personnel may now move freely", tweeted Naval Support Activity Bethesda. US Navy tweeted that it was an "ad hoc drill by tenant command", Xinhua news agency reported.

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.

US Congressman Dutch Ruppersberger 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.