Rescue workers in Baltimore are searching for about 20 people and multiple vehicles believed to have fallen into the Patapsco River after a major bridge at the city's port was struck by a large ship, a Fire Department spokesperson told CNN.

The official warned that the collapse of the Francis Scott Key Bridge was a "mass casualty multi agency incident," and conditions were unsafe for rescuers due to "some cargo or retainers" hanging from the structure, freezing conditions and limited visibility.

Video footage shows the collapse of the 1.6-mile-long, four-lane bridge after it was hit by the vessel.

The bridge extends over the Patapsco River and serves as the outermost crossing of the Baltimore harbor. It is an essential link of Interstate-695, or the Baltimore Beltway.

Source: CNN