Authorities are investigating the cause of an explosion aboard a cargo ship that was leaving the Port of Baltimore when it issued a mayday call.

The blast happened near the site of last year's deadly Francis Scott Key Bridge collapse, the Coast Guard said, and the resulting fire was extinguished.

An explosion on a cargo ship carrying coal was heard throughout Baltimore's harbor on Monday night, prompting a distress call. The explosion was close to the site of last year's collapse of the Francis Scott Key Bridge, and caused the city's main shipping channel to be closed on Tuesday morning.