The U.S. Coast Guard closed marine traffic into and out of the Port of Baltimore for more than 20 hours for safety concerns.

Investigators on Tuesday were trying to determine what caused an explosion aboard a cargo ship laden with coal as it departed Baltimore's harbor for East Africa.

According to the Coast Guard, the 751-foot Liberia-flagged vessel was sailing outbound from Baltimore Harbor with 23 crew members and two pilots aboard when the explosion occurred around 6:30 p.m. Ea...