Secretary of Homeland Security Alejandro Mayorkas said "there are no indications this was an intentional act," adding, "we are assessing the impacts to the Port of Baltimore."

"Our thoughts are with the families of the missing and injured," he said.

The Coast Guard is "actively involved in search and rescue operations," he said.

The 1.6-mile bridge on the I-695 beltway crosses the Patapsco River, where Francis Scott Key was inspired to write the words of the U.S. national anthem in 1814, according to the Maryland Transportation Authority.

Key, after whom the bridge was named, was also an advisor to Andrew Jackson, served as the District Attorney for the District of Columbia from 1833 to 1841, and was a slave owner, according to the National Park Service.

Construction on the bridge, which was intended to ease traffic and maintenance concerns regarding the Baltimore Harbor Tunnel that serviced the waterway, began in 1972 and finished in March 1977, according to the MDTA.