"The fear is that the boat the Brazilians were traveling in went down in the Caribbean as it left the Bahamas," according to Brazilian authorities on the official government information website, Portal Brasil.
The migrants' families have not heard from them since November 6, the Brazilian foreign ministry said.
Brazilian media reports said there were also dozens of other migrants aboard the boat, which officials suspect went down while attempting the roughly 50-mile (80-kilometer) crossing between the Bahamas and the Florida coast.
The Brazilian foreign ministry said it was not ruling out the possibility that the migrants could be in prison or missing for other reasons.