Rescue teams have been scouring the Atlantic off Florida's coast as they continue to search for 39 people who have been reported missing by a survivor who clung onto a boat that capsized.
The US Coast Guard suspect the boat was part of a human smuggling bid that went badly wrong.
The survivor told authorities after his rescue that he had left the Bahamas' Bimini islands, about 50 miles east of Miami, in a boat with 39 other people on Saturday night, the Coast Guard tweeted.
The boat capsized in rough weather about 45 miles east of Fort Pierce Inlet, off Florida's Atlantic coast, about midway between Miami and Cape Canaveral.
The Coast Guard added that the survivor revealed nobody had been wearing life jackets.
A good Samaritan found the man perched on the mostly submerged hull of the overturned boat on Tuesday morning and rescued him before alerting the Coast Guard.
They sent cutter vessels and aircraft to search an area stretching from Bimini to Fort Pierce Inlet for the missing.
The potential loss of life stemmed from "a suspected human smuggling venture," the Coast Guard said in its statement.
The nationality of those on board has yet to be determined, a Coast Guard spokesperson, Petty Officer Jose Hernandez, said.
It comes after another ill-fated crossing attempt that ended with 32 people rescued from a capsized vessel last Friday, west of Bimini.
The area has become frequent transit point for sea-going smugglers, Hernandez said.
Incidents of overturned or interdicted vessels crowded with people, many of them Haitians or Cubans seeking to reach the United States, are not uncommon in the waters off Florida.
In May, last year, 12 Cuban migrants perished and eight were rescued after their boat flipped over off Key West, Florida.
At least 557 Cuban migrants in all have been picked up at sea by the Coast Guard since October, in addition to nearly 7,400 Cubans interdicted during the previous five years, according to the agency.
Vessel crossings of Haitian migrants have likewise grown more frequent as the Caribbean island nation deals with economic and political crises, as well as gang-related kidnappings.
The Coast Guard said it had intercepted at least 159 Haitian nationals this year.
Last week, 90 people were repatriated to the Dominican Republic, which shares the island of Hispaniola with Haiti, following rescue and interdiction of three illegal voyages across the Mona Passage near Puerto Rico.
