Rescue teams have found one body in their search for 39 people reported missing after their boat capsized off Florida’s coast, the US Coast Guard says in what is being called a human smuggling attempt gone awry.

Coast Guard Commander Jo-Ann Burdian said search and rescue efforts would continue for survivors, a day after a good Samaritan rescued a man perched on the mostly submerged hull of the overturned boat in the Atlantic Ocean.

“We do suspect that this is a case of human smuggling, as this event occurred in a normal route for human smuggling,” Ms Burdian said, adding that US Homeland Security officials were investigating the incident.

Ms Burdian said a cutter crew found the deceased person.

She said information about the person would not be released until their family was informed.

The good Samaritan, who was on a commercial vessel, alerted the Coast Guard, which dispatched rescue vessels and aircraft to search for more victims.

The Coast Guard said the survivor told authorities he had left the Bahamas’ Bimini islands, about 80km east of Miami, in a boat with 39 other people on Saturday night.

According to the survivor, the group’s vessel capsized on Sunday morning when it hit rough weather about 72km east of Fort Pierce Inlet, off Florida’s Atlantic coast about midway between Miami and Cape Canaveral, but no one was wearing a life jacket, the Coast Guard said.

The U.S. Coast Guard ship Bernard C. Webber searches for the missing people. Photo: AAP

The survivor was taken to a hospital for treatment of dehydration and sun exposure.

The accident coincided with a small-craft advisory posted for the area, with steady winds clocked at up to 37km per hour and 3-metre seas, according to the Coast Guard.

“Their decision to take to the sea is a complicated one. Certainly, the waters in the northern Florida Straits can be quite treacherous,” Ms Burdian said.

US Coast Guard Captain Jo-Ann F. Burdian. Photo: AAP

“In cases like this, small vessels, overloaded, inexperienced operators, at night in bad weather can be incredibly dangerous.”

Through Wednesday morning, Coast Guard cutter crews, helicopter teams, search planes and a US navy air crew crisscrossed an area spanning more than 7,500 nautical miles about the size of Rhode Island, between Bimini and Fort Pierce Inlet, the statement said.

The nationalities of those who were aboard the vessel has yet to be determined, Petty Officer Jose Hernandez said.

Incidents of overturned or interdicted vessels crowded with people, many of them Haitians or Cubans seeking to reach the US, are not uncommon in the waters off Florida.