BETHESDA, Md. (WJZ) —The U.S. Navy says a mistake using a mass notification system led to reports of an active shooter at Walter Reed National Military Medical Center.

They said the false alarm was the result of “improper use of a mass notification system”.

A call came in at about 2 p.m. for a report of an active shooter situation in the basement of building 19 at Walter Reed. After an investigation by NSA Bethesda, no active shooter was found.

Security responded and cleared the building, finding no indication of an active shooter. After investigating the call and the origin, NSA Bethesda has determined that this was a false alarm and not part of a scheduled drill as has been reported. 2/2 — NSABethesda (@nsabethesda) November 27, 2018

Investigators found that this was a “false alarm and not part of a scheduled drill,” as was reported by the U.S. Navy and other military officials.

The U.S. Navy tweeted later in the evening that the incident was the result of “the improper use of a mass notification system by a tenant command aboard the installation,”

The active shooter event aboard Naval Support Activity Bethesda today was the result of the improper use of a mass notification system by a tenant command aboard the installation. While preparing for an upcoming drill, the notification system was inadvertently enacted… (1/3) — U.S. Navy (@USNavy) November 27, 2018

They continued to say that while preparing for an upcoming drill, the notification system was “inadvertently enacted without containing the words “EXERCISE” or “DRILL”

…without containing the words "EXERCISE" or "DRILL." Individuals who saw the mass notification statement immediately notified NSA Bethesda security, where they responded accordingly and instituted an installation-wide active shooter response. … (2/3) — U.S. Navy (@USNavy) November 27, 2018

They said on further investigation, they determined that the improper use of the system was the root cause and secured from the active-shooter response.

CONFIRMED: No active shooter at Naval Support Activity Bethesda. Was ad hoc drill by tenant command. https://t.co/P9N65mMdOA — U.S. Navy (@USNavy) November 27, 2018

Maryland Rep. Dutch Ruppersberger was there for a doctor’s appointment.

He said, “at no point was there any indication that this was a drill.”

The congressman said he waited with 40 people who heard active shooter announcements blaring inside the facility.

“I was walking the halls and all of a sudden people who work for the hospital we’re telling us to get in this back room…and then they barricaded the doors,” Ruppersberger said. “About every 20 minutes, an announcement would come on and say ‘There’s an active shooter. Security is on the premises.’ They eventually let us go and said it was ok. We went out in the hall, and they put us back in the room again.”

We've been given the all clear at Walter Reed – at no point was there any indication that this was a drill. — Dutch Ruppersberger (@Call_Me_Dutch) November 27, 2018

1/3 If today’s active shooter investigation at Walter Reed Medical Center was a drill, I clearly did not get the memo and neither did the other people who were told to shelter in place with me, nor did Montgomery County Police and other agencies… — Dutch Ruppersberger (@Call_Me_Dutch) November 27, 2018

Ruppersberger tweeted about an active shooter at Walter Reed around 2:31 p.m. and said he was sheltering in place.

“I am currently at Walter Reed Medical in Bethesda where we’ve been told there is an active shooter. I am currently safe in a conference room w/ approx 40 others,” Ruppersberger tweeted out.

I am currently at Walter Reed Medical in Bethesda where we've been told there is an active shooter. I am currently safe in a conference room w/ approx 40 others. — Dutch Ruppersberger (@Call_Me_Dutch) November 27, 2018

Another tweet from Ruppersberger’s account at 3:04 p.m. stated that he remains sheltered and he again confirmed he didn’t believe it to be a drill.

“Rep. Ruppersberger remains sheltered in a back room at Walter Reed. Described mood as calm. Has not been given any additional details but does not believe this to be a drill.”

Rep. Ruppersberger remains sheltered in a back room at Walter Reed. Described mood as calm. Has not been given any additional details but does not believe this to be a drill. — Dutch Ruppersberger (@Call_Me_Dutch) November 27, 2018

Ruppersberger said he wants answers as to how this happened.

“There were people who were very upset and afraid. There are a lot of people who really had serious issues,” He said. “The fact that I’m a member of Congress—and I’m on the Defense Appropriations Committee—I’m going to check with the Defense Department to find out who was in charge of this and why did happen this way because people could’ve been hurt. It was a lot of anxiety that we didn’t need to have,”

Outside the facility, a massive police response could be seen from Chopper 13 as cars waited to enter the facility were lined outside.

The building was locked down.

“We locked down everything, cut off the lights make sure nobody was in the hallway. We were pretty prepared,”

[WJZ Reporter:] “Was there a little bit of panic when this alert came across your phone?”

“Yes. Always is. Any time you have a surprise of any type it’s always a hit of panic, but we all worked together as a team,” said

The Montgomery County Police Department also responded to the scene to help with the investigation.

MCP has been called to assist with the report of a possible active shooter at the Walter Reed Nat Mil Med Ctr located at 8901 Rockville Pike. More information will be released as it is confirmed. Call received to assist – 2:23 pm. — Montgomery Co Police (@mcpnews) November 27, 2018

People inside the facility were scared and sheltering in place after receiving text alerts and emails about an active shooter.

Active Shooter at my job. Walter Reed Hospital. pic.twitter.com/ee3fXlqO6K — A'Jada 🧡 (@nattyby__nature) November 27, 2018

Here’s a copy of text sent to employees at Walter Reed earlier today. All clear just issued. @wjz pic.twitter.com/3NJzZLTxTN — Avajoye Burnett (@AvajoyeWJZ) November 27, 2018

Inside Walter Reed right now after the active shooter announcement. Was looking on Twitter for news and it's filled with people questioning the safety of their loved ones. Building 19 in lockdown. Haven't heard any shots. Multiple agencies responding. Hopefully false alarm. pic.twitter.com/xNDKyEuN56 — Lindsey Migliore, DO (@DrMigliore) November 27, 2018

“I’m going to check with the defense department and find out who was in charge of this, why did it happen this way, because people could have been hurt,” Ruppersberger said.

Follow @WJZ on Twitter and like WJZ-TV | CBS Baltimore on Facebook