Coast Guard says it has found four additional bodies from 39 migrants lost at sea off Florida but will end its rescue operations at sunset if it doesn't receive any new information.

US Coast Guard searched for several days to find 39 people missing from a capsized boat after a solitary survivor was found clinging to the overturned hull.
US Coast Guard searched for several days to find 39 people missing from a capsized boat after a solitary survivor was found clinging to the overturned hull. (AP)

The US Coast Guard has called off the search for dozens of people missing from a boat that capsized off Florida last weekend in a suspected human smuggling tragedy.

Search teams have recovered five bodies so far, from around 40 people who were on the boat, according to the military branch.

Coast Guard captain Jo-Ann Burdian said that if the force does not receive new information to narrow its search, active search efforts will end at sunset on Thursday.

"Unfortunately we've come to the most difficult time in any search and rescue case and that is the point at which we decide when to cease actively searching," Burdian told a news conference before the mission was aborted.

End to rescue efforts leaves 34 people missing five days after the vessel capsized on the way to Florida from Bimini, a chain of islands in the Bahamas about 88 kilometres east of Miami.

Burdian said the decision to suspend the search at sunset, pending any new discoveries, was not an easy one.

"We have saturated the area over and over again." 

"We've had good visibility. ... We've overflown the vessel a number of times. ... It does mean we don’t think it’s likely that anyone else has survived," she added.

READ MORE: Dozens missing after boat sinks off US coast

Investigation into human smuggling

The Miami office of Homeland Security Investigations has launched an inquiry, saying the migrants' journey was most certainly part of a human smuggling operation. 

Under federal law, a smuggler convicted of causing death is eligible for execution.

"The goal of this investigation is to identify, arrest and prosecute any criminal or criminal organisation that organised, facilitated or profited from this doomed venture," said HSI Miami Special Agent in Charge Anthony Salisbury.

Salisbury declined to give any information on the nationalities of the boat passengers but said investigators consider the lone survivor "a victim right now," not a suspect. Salisbury appealed to the public for tips to help identify who organised the boat crossing.

The lone survivor was found hanging onto the 25-foot vessel about 64 kilometres off Fort Pierce, Florida. He told a good Samaritan and authorities that the boat capsized late on Saturday after he and 39 others had set out for Florida from Bimini.

Authorities said the boat was found about 160 kilometres north of where it capsized, apparently pushed by the Gulf Stream, a warm, swift current that wraps around the Florida peninsula and flows along the Atlantic Coast of the United States. No one was wearing a life jacket, the rescued man told authorities.

The Gulf Stream can be treacherous even on a calm, sunny day. Throw in an overloaded boat, inexperienced mariners, stormy weather and the dark of night, and they can become deadly.

A small craft advisory had been issued on Saturday and Sunday as a severe cold front with winds up to 37 kph blew through the dangerous passage, creating swells up to 3 metres.

READ MORE: Several dead as suspected smuggling boat capsizes off San Diego

Source: AFP