Updated 1:04 p.m. | Shortly after 1 p.m. Thursday a loud bell rang followed by a loudspeaker announcement reopening the Cannon House Office building after an evacuation order that lasted more than an hour.

Cannon was evacuated Thursday morning when alarms sounded.  

Capitol Police and the Architect of the Capitol investigated the issue determined that a malfunctioning electrical panel was the cause. There were no reports of smoke or fire, according to a Capitol Police statement.

The House is in recess and most lawmakers are back in their districts ahead of the midterm elections.

Staff were required to show their congressional ID to re-enter the building. IDs are not typically required to enter, which left dozens of staffers outside calling colleagues to deliver their IDs to them from inside. 

Watch: Cannon House Office Building Evacuated

Security concerns have been elevated on Capitol Hill following the discovery of pipe bombs mailed to prominent Democrats, including Rep. Maxine Waters.

Massachusetts Democratic Rep. Jim McGovern’s communications director tweeted from the scene.

“Cannon House Office Building being evacuated right now. No details. Alarms went off and we were told to evacuate immediately,” Matt Bonaccorsi said.

Cannon House Office Building being evacuated right now. No details. Alarms went off and we were told to evacuate immediately.

— Matt Bonaccorsi (@MattBonaccorsi) October 25, 2018

Tourists repeatedly asked what was happening. Staffers, who only knew they were told to leave the building, hesitated to even reveal that an alarm had sounded.

U.S. Capitol Police cordoned off the exterior of the building with police tape and positioned officers around the perimeter, which is not standard practice during fire drills or false alarm evacuations. Inside, the tunnel connecting Cannon to the Capitol is closed.

USCP sent out an alert saying an investigation was ongoing and directing staff and personnel to remain in an assembly area and await further instruction. It also announced the following road closures:

• Independence Avenue from Washington Avenue SW to First Street SE
• Westbound traffic on Independence Avenue from First Street to Second Street SE
• C Street from Second Street to New Jersey Avenue SE
• New Jersey Avenue from Independence Avenue to D Street SE

Cannon is the oldest congressional office building, built in 1908. The building is currently undergoing a full renovation, expected to take 10 years and cost approximately $752.7 million.

Niels Lesniewski contributed to this report.