The overturned skiff, whose initial number of occupants is not known – migrants according to the authorities – was spotted at midday with several people in the water who did not appear to be equipped with life jackets. safety.
The coast guards then dispatched several helicopters and a boat to the area concerned, about 18 km from the desert island of Desecheo, west of Puerto Rico.
As of 6 p.m. (2200 GMT), rescuers had rescued 11 women and 20 men, according to Coast Guard spokesman Ricardo Castrodad.
US border police had earlier clarified that they were mainly migrants from Haiti and the Dominican Republic. The coast guards had indicated in a press release that they “suspected” the ship “of having undertaken an illegal crossing”.
The search, which also involves teams from the police and the Puerto Rican coast guard, is continuing, said Ricardo Castrodad.
The desert island of Desecheo sits in the Mona Channel between Puerto Rico and the island of Hispaniola, which includes Haiti and the Dominican Republic.
A Haitian woman had already lost her life there on Saturday, after the sinking of a boat carrying 69 migrants.
Hundreds of Haitians managed to reach Florida during the month of March, while more than a hundred had been intercepted near the Bahamas by the American Coast Guard.
Haiti, the poorest country on the American continent, is going through an acute crisis aggravated by growing insecurity and the corruption of its institutions.