Washington DC - The Walter Reed hospital outside Washington, which treats military personnel and US presidents, was briefly locked down Thursday after reports of an active shooter.

The emergency ended after authorities made an arrest of a man who turned out to be carrying an imitation firearm, the police in Montgomery County, Maryland, where the facility is located, said on social media.

"There is no threat to the community and the scene is secure," they added.

In another post shared on X, law enforcement officials confirmed that the individual carrying what was later revealed to be a training rifle had "no malicious intent" and would not be facing any charges.

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Earlier, the Navy unit running the complex announced that "security is responding to reports of a potential active shooter" and said "the installation remains on lockdown."

The sprawling Walter Reed Medical Facility treats wounded military personnel and houses a hospital dedicated to treating US presidents and conducting their annual check-ups.