Rescuers search for survivors after 11 dead in Puerto Rico boat wreck
The US Coast Guard said it was working in conjunction with US Customs and Border Protection and Puerto Rican authorities to rescue survivors(AFP)

At least 11 people died after a boat believed to be carrying dozens of migrants capsized off the coast of Puerto Rico, with rescue efforts set to continue through the night, the US Coast Guard said on Thursday.

"As of 6 PM Thursday (2200 GMT), responding partner agency units have rescued 31 survivors, 11 female and 20 male. 11 deceased have been recovered," the Coast Guard said in a tweet.

A spokesperson for US Customs and Border Protection (CBP) told AFP that the shipwreck occurred 10 nautical miles (19 kilometers) north of Desecheo Island, an uninhabited US territory between Puerto Rico and the Dominican Republic.

The spokesperson said most of the survivors were from Haiti or the Dominican Republic.

The US Coast Guard said rescuers were searching for survivors "with all available assets, including helicopters, airplanes and rescue boats", and were working in conjunction with CBP and Puerto Rican authorities.

Images released by the agency showed several survivors huddled together on a piece of floating debris, while others were dragged on board rescue boats.

Survivors were flown to a US Coast Guard base in Puerto Rico to receive treatment, a statement said.

Earlier, the agency said that the capsized vessel was suspected of "taking part in an illegal voyage," but did not elaborate.

A CBP helicopter first spotted the boat and a number of people in the water who appeared not to be wearing life jackets around midday on Thursday (1600 GMT), the statement said.

Multiple rescue helicopters were launched and a Coast Guard vessel was diverted to assist in the recovery.

"The search for survivors is scheduled to continue through the night," the US Coast Guard said in a Thursday evening tweet.

In March, hundreds of Haitians landed in sailboats on the Florida coast while over 100 were intercepted off the Bahamas by the US Coast Guard.