At least 11 suspected migrants have died after their boat capsized near the US territory of Puerto Rico.
The US Coast Guard said there were 38 survivors so far - mostly from Haiti, with two from the Dominican Republic.
Interceptions of migrants in the waters of the Caribbean have spiked in the past year.
"The sea is dangerous," said Rear Admiral Brendan McPherson from the US Coast Guard. "These ventures are dangerous."
The Coast Guard first learned of the capsize after the ship - which was taking part in an "illegal voyage" - was spotted by a Customs and Border Patrol aircraft about 10 nautical miles (18km) off the coast of Desecheo, an uninhabited island in Puerto Rico.
The boat's passengers did not appear to be wearing life jackets, the Coast Guard said. The vessel is believed to have departed from the Dominican Republic.
In a statement on Thursday night, Rear Adm McPherson said they were searching for survivors with boats, helicopters and fixed-wing aircraft.
"Our highest priority is saving lives and that is what my crews will exhaust themselves doing," he said.
