UPDATE, 1:30 p.m. EDT: Montgomery County Police Capt. Paul Starks told reporters Monday afternoon there were no injuries reported from the alleged shooting. "We haven't confirmed that it's a gunshot, but just that it's the sound," NBC4 Washington reported he said.
Police were continuing to sweep the center, and the lockdown remained in place. Non-emergency patient services were suspended for the rest of the day.
Authorities are investigating a report of a single gunshot fired Monday morning at Walter Reed National Military Medical Center in Bethesda, Maryland. Mongtomery County Police tweeted that they received a 911 call at 10:48 a.m. EDT but had not been able to confirm the incident. The center has been on lockdown since.
"All base personnel are sheltering in place as a result of unconfirmed reports of an active shooter," a statement from the Navy read. "DOD Security Force, NIH Police Force and County EMS and Medics have responded and are searching the area."
The Walter Reed center in Bethesda, just outside Washington, D.C., is one of the largest military hospitals in the U.S. It has about 8,500 employees, according to its website.
People Monday were tweeting while on lockdown:
please be a drill.
— Cat (@Jungle_CAAT) July 6, 2015
Active shooter -Walter reed. Huddling in place with my patients. #activeshooter
— Tiffany Angelo (@tea2121) July 6, 2015
Still nothing new here at Walter Reed
â€” Devante Brooks (@_DevanteBrooks) July 6, 2015
please keep me and the rest of Walter Reed staff in your prayers, this situation is still unconfirmed
â€” marissa (@mareezy527) July 6, 2015