The death toll from the Friday capsizing rose to six, Fernando Castillo, provincial director of Dominican Civil Defense, told AFP.

The boat was headed for the US territory of Puerto Rico carrying between 40 and 50 people, with 17 rescued.

Among the bodies recovered so far were a woman, three men and a child. The deceased are Dominican and Haitian nationals.

Strong waves, large amounts of sargassum seaweed and dust clouds blowing in from the Sahara desert were hampering the search efforts, said Civil Defense Director Juan Salas.

"Today the biggest concern is the sargassum, which makes it difficult to see any body or any element in the water," the official told AFP.

The Dominican Navy said the migrants "were trying to travel illegally to Puerto Rico" from the eastern end of the Dominican Republic, near Punta Cana.

They were being ferried in a so-called "yola" boat, which are generally constructed from wood or fiberglass and do not comply with safety regulations, according to authorities.

Migrants pay as much as $7,000 for a one-way trip to Puerto Rico from the Dominican Republic, which shares the island of Hispaniola with crisis-torn Haiti.

The irregular migration route has become increasingly popular in the last decade.