The explosion knocked a 30-ton steel hatch off the vessel, but its exact underwater location was unknown, the Coast Guard said Tuesday afternoon.

An apparent explosion on a ship in the Baltimore Harbor near the site of the Key Bridge has been fully contained, according to Baltimore City fire officials.

The Port of Baltimore’s main shipping channel was closed for several hours Tuesday while crews worked to locate a hatch from the ship that detached during the explosion and fell into the water, offici...