Two people were dead and eight survivors were rescued from waters off the Florida Keys, U.S. Coast Guard officials said Friday.
Authorities continued to search for another five people who are still in the water, they said.
The 15 people, all thought to be migrants, were on board "a rustic vessel on an illegal voyage," the Coast Guard said in a statement.
The boat capsized about 14 miles south of Sugarloaf Key, and rescuers were informed of the migrants' distress about 10 a.m., the military branch said.
It was not clear from where they had traveled. U.S. Coast Guard officials said U.S. Customs and Border Protection was among the agencies that responded to the situation.
"This incident off the coast of the Lower Keys remains under investigation," CBP spokesperson Rob Brisley said by email. "CBP has nothing further to add."
The Coast Guard said people on a cruise ship rescued one migrant. A photo of the scene released by the agency Friday shows Royal Caribbean's Mariner of the Seas.
Rescues were also made by other good Samaritans and Coast Guard "partner agencies" in the area, it said in a statement Friday evening.
The deceased were pulled from the water by Florida Fish and Wildlife Conservation officers and transferred to a local medical examiner's office for identification, the Coast Guard said.
Among the eight rescued, two were "in good health," but six others needed emergency medical attention, it said. Their conditions were unavailable.
The seas off Florida's southern coast are well known for being a conduit for Cuban migration to the United States, and are now host to the largest exodus from the island nation since the Mariel Boat Lift of 1980.
Experts say political turmoil and economic hardship, including inflation and a shortage of basic goods, are driving U.S. hopefuls into the Straits of Florida.
It's a journey — made on dinghies, rafts and makeshift floatation devices — that regularly claims lives.
Chief Patrol Agent Walter N. Slosar of the U.S. Border Patrol’s Miami Sector said Friday that agents and other law enforcement officers have arrested 108 Cuban migrants at 12 landings in the Florida Keys in the last two days.
Last month, CBP reported that its agents, with the help of the Coast Guard, rescued 23 migrants in waters off Marathon, Florida. In June, CBP, the Coast Guard, and local law enforcement agencies rescued 38 Cubans stranded on remote Florida Keys islands, according to a CHP statement.
Rear Adm. Brendan McPherson, commander of the Coast Guard's southeastern operations, said in the agency's statement that Cuban migrants are often found at sea without life jackets "on unseaworthy or overloaded boats and homemade rafts."
"Our search continues for others that may have survived this tragic incident," he said. "This situation highlights the risks these migrants face as they attempt to enter the United States illegally by sea."