Police in Maryland there is "no indication" of an active shooter situation in the area near Walter Reed National Military Medical Center, despite emergency calls regarding hearing gunshots.

The hospital is located just outside of Washington, DC in Bethesda, Maryland but Naval Support Activity Bethesda tweeted there was no imminent danger to patients and staff.

US Congressman Dutch Ruppersberger of Maryland tweeted he is at the centre but "currently safe in a conference room w/ approx 40 others."

Swat teams were seen swarming the building complex but NSAB public affairs officer Jeremy Brooks told the Associated Press "right now there is no indication that there is any active shooter, but we won't know 100 percent until the buildings have been successfully cleared."

Mr Ruppersberger's staff appears to have taken over his Twitter account and said the congressman "does not believe this to be a drill". However the Pentagon later confirmed it was, in fact, a drill to test security response.

The south gate to Walter Reed had been closed as police continue to investigate the situation.

Mass shootings in America Show all 8 1 /8 Mass shootings in America Mass shootings in America Camden shootings – 1949 Howard Unruh killed 13 people, including three children, during a 12-minute walk through his neighborhood on September 6, 1949, in Camden, New Jersey, when he was 28 years old. The incident became known as the "Walk of Death". Unruh was found to be criminally insane and died in 2009 after a lengthy illness at the age of 88, following 60 years of confinement. Alamy Mass shootings in America University of Texas tower shooting – 1966 Charles Whitman killed 17 people and injured 31 others in Austin, Texas. After stabbing his mother and wife the night before, he headed to the University of Texas, where he opened fire on people in the campus and streets from the observation desk. He was shot dead after a policeman and civilian reached the scene. Austin History Center, Austin Public Library Mass shootings in America Easter Sunday Massacre – 1975 James Ruppert killd 11 family members in his mother's house, which included his mother, brother and his wife, as well as their eight children. He used a magnum, two handguns and a rifle. Mass shootings in America Wilkes-Barre shootings – 1982 Former prison guard, George Banks, shot dead 13 people in Pennsylvania, including five of his own children. AP Photo/Times Leader Mass shootings in America Wah Mee massacre – 1983 Three men, Kwan Fai Mak, Wai-Chiu Ng, and Benjamin Ng, killed 13 people who were in Seattle's Wah Mee gambling club. YouTube/KIRO 7 News Mass shootings in America San Ysidro McDonald's massacre – 1984 James Huberty killed 21 people and injured 19 others after he walked in a McDonald's in San Diego. He was shot dead by a sniper after 78 minutes of him entering the restaurant. Alamy Mass shootings in America Palm Sunday massacre – 1984 Ten people were shot dead from handguns at close range in a New York home. A baby girl was the only survivor after convicted dealer, Christopher Thomas, shot three women, one teenage girl and six children in their Brooklyn home. Thomas was convicted of manslaughter and cleared of murder. He was released from prison after 32 years. Mass shootings in America Edmond post office shooting – 1986 Patrick Sherrill, a postal worker at the Edmond post office in Oklahoma, killed 14 co-workers and injured 6 others, before he shot himself. Oklahoma Highway Patrol Collection

Police have not reported finding any victims despite several 911 calls indicating people had heard gunshots in the vicinity. The main road leading to the centre has also been cleared of traffic out of precaution.

Police have reportedly cleared the basement of Building 19 in the complex, but did not find a shooter.

The whole building had been cleared out of precaution as service members recover from injuries and get medical treatment.