Round-the-clock search operations were halted at nightfall on Thursday, Coast Guard Petty Officer Jose Hernandez said, hours after US authorities reported recovering four more bodies, bringing the tally of confirmed fatalities to five.

A lone survivor was rescued on Tuesday morning after a tug boat 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 2400 square kilometres of open sea off Florida's Atlantic coast.

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

He was picked up about 70km 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 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 on Thursday.

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 by way of the Bahamas, a known hub for seaborne human smuggling.

Australian Associated Press