Three migrants drowned and 354 were rescued from dinghies in Spanish waters on Friday, the maritime rescue service said.
The nationalities of the dead and rescued were not immediately known.
Spain has become the main entry point for migrants fleeing Africa to seek a better life in Europe, overtaking Italy and Greece, as Italy's new populist government refuses to admit rescue boats.
The Spanish coastguard found the three bodies and rescued 35 people from a sinking dinghy in the sea of Alboran in the western Mediterranean, after the vessel was spotted by a rescue plane, a spokesperson said.
As of Friday afternoon, a total of 354 people had been rescued from nine boats in Spanish waters.
While the numbers of people migrating are down across Europe, Spain has seen a sharp increase in arrivals this year.
A total of 35,218 migrants had entered Spain by sea so far this year by the end of September, Interior Ministry data shows. This is more than three times the number for the same period last year.