Bricks of the white powdery substance were stuffed in duffel bags found in a shipping container aboard the MSC Desiree, which was traveling from Colombia to Europe, the source told ABC News.
Federal and local authorities inspected the container after noticing the bolts on the door had been tampered with, the source said.
The total amount of cocaine, approximately 992 pounds, has a street value of about $18 million, and is the most ever seized in Philadelphia, according to the source.
Last week, authorities confiscated 3,200 pounds of cocaine, with a street value of $77 million, that had been hidden behind boxes of dried fruit aboard a cargo ship at the Port of New York and New Jersey. It was the largest coke bust at the port in a quarter century.
Federal agents have been paying closer attention to tampered shipping containers as cocaine makes a comeback amid rising crop production in Colombia, which is no longer eradicating coca plants, the source told ABC News.