The US Coast Guard has called off a three-day search for 34 people lost at sea off Florida from a boat that capsized while engaged in what officials suspect was an attempt to smuggle migrants into the United States from the Bahamas.

Round-the-clock search operations were ended at nightfall, hours after US authorities reported recovering four more bodies, bringing the number of confirmed fatalities to five.

A lone survivor was rescued on Tuesday morning after a tugboat crew found him clinging to the mostly submerged hull of the overturned boat.

He said none of the 40 people aboard had been wearing life jackets.

Since then, a small armada of Coast Guard and Navy vessels and aircraft have crisscrossed at least 1,500 square miles of open sea off Florida's Atlantic coast.

Captain Jo-Ann Burdian, commander of the Coast Guard's Miami sector, said that the quest for more victims would be "suspended" at sunset "if we don't receive additional specific information to help redirect our search".

Asked if the remaining 34 missing migrants should be presumed dead, Captain Burdian said: "It does mean that we don't think it's likely that anyone else has survived."

Captain Jo-Ann Burdian, commander of the US Coast Guard's Miami sector

The survivor told authorities the ill-fated vessel left the Bahamas' Bimini islands, about 80km east of Miami, on Saturday night, and capsized the next morning in rough seas.

He was picked up about 72km east of Fort Pierce Inlet, off Florida's Atlantic coast, about midway between Miami and Cape Canaveral.

The Coast Guard and US Homeland Security Department officials have said the vessel was involved in a human smuggling attempt, but the nationalities of those on board have not been disclosed.

Anthony Salisbury, the agent in charge of the Homeland Security Investigations office in Miami, said it had opened a criminal inquiry seeking to prosecute anyone who organised or profited from the venture.

In a separate incident, the Coast Guard reported intercepting a sailing vessel on Tuesday off another area of the Bahamas overloaded with 191 Haitian migrants believed to be headed for Florida.

The Coast Guard said 189 people on that boat were turned over to Haitian authorities yesterday.

A mother and her child were transferred ashore to Port-au-Prince, the Haitian capital, for medical treatment on Tuesday, the day the boat was interdicted, the Coast Guard said.

Voyages of vessels carrying Haitian migrants have grown more frequent as the Caribbean island nation faces worsening economic and political crises, as well as gang-related kidnappings.

The two incidents underscored a surge in migrants seeking passage to Florida in flimsy vessels through the Caribbean byway of the Bahamas, a known hub for seaborne human smuggling.