Officials warned residents near Fort McHenry National Monument that they may hear a loud noise Friday night and urged them to avoid the area as crews worked to neutralize an explosive device found hours earlier at the Baltimore landmark.

Fort McHenry was shut down Friday afternoon after renovation crews unearthed a cannonball buried beneath the historic site, drawing a bomb squad response and halting work there.

The Baltimore Police Department’s Hazardous Device Team and Air Force Explosive Ordnance Disposal technicians were called and continued working at the site Friday night.

Police said natural gas service in the immediate area has been shut off while crews secure the device.

Shannon McLucas, a spokesperson for the National Park Service, said all visitors and staff were safely moved outside of the area. No injuries were reported.

Baltimore Fire Department spokesperson John Marsh confirmed a cannonball was discovered.

The Baltimore Police Department sent its bomb squad as a safety measure, said Vernon Davis, a spokesperson for the department.

Davis said the device was not modern or recently planted, and that it was found underground.

On Friday afternoon, “evidence of buried historic ordnance was discovered by National Park Service preservationists,” the park said in social media posts. The park shut down just before 1 p.m. and will reopen after officials deem it safe, according to the posts.

Police blocked off the end of East Fort Avenue on Friday afternoon.

The area where Fort McHenry stands served as an active military base during several wars, including the American Revolution, the War of 1812 and the Civil War, according to the National Park Service. Because of this, McLucas said, Friday’s discovery wasn’t uncommon.

Fort McHenry, which sits on the end of the South Baltimore neighborhood of Locust Point, reopened one week ago after the federal government shutdown forced it to close for over a month.