After the Panama-flagged Seaboard Trader moored at the port Monday night, two additional stowaways were transported to a Miami hospital, said Lt. Cmdr. Chris O'Neil, spokesman for the U.S. Coast Guard's 7th District.
The four men were found inside a shipping container aboard the vessel, which was carrying merchandise for Sara Lee Branded Apparel, said Port of Miami spokeswoman Andria Muniz.
The reason the two men died was under investigation. The four men were all believed to be Dominican nationals, O'Neil said.
The vessel had departed Saturday from Puerto Plata, on the north coast of the Dominican Republic.
The Seaboard Trader reported to U.S. authorities around 7:15 a.m. Monday that its crew had discovered the stowaways while still more than 100 miles off Florida's coast, said O'Neil.
The 40-foot long container in which the stowaways were found contained T-shirts and had been packed in Haiti before being loaded onto the vessel in the Dominican Republic, O'Neil said.
"From what we can tell, if they were in the container when it was loaded, they would have been in the container for four days," O'Neil said. "But the mechanics of how they got in, when they got in, is still under investigation."
The ship is owned by Miami-based Seaboard Marine, said Zachary Mann, Customs and Border Protection spokesman.
Telephone calls made after hours to the company's offices rang unanswered.
Officials at Jackson Memorial Hospital in Miami said they would not release the condition of the two stowaways being treated there without their consent.
Stowaways are typically sent back to their port of origin, Mann said.