The bodies of at least 20 people have been pulled from the sea off the coast of Melilla, a small Spanish territory bordering Morocco.
Moroccan rescue services recovered the corpses after the crew of a passenger ship spotted them in the water.
The dead are believed to be migrants from sub-Saharan Africa.
It is thought they may have been hoping to reach Europe by trying to land in Melilla, despite storm warnings being issued for the region.
Melilla, which is just 12 sq km (7 square miles), is a major crossing point for migrants seeking work or asylum in Europe.
Together with a second Spanish enclave, Ceuta, it is the EU’s only land border with Africa.
Spanish newspaper El Pais reports that the bodies were found floating around 6-8km from Melilla’s coast.
The exact death toll has not yet been confirmed. Spanish rescue services resumed a search on Sunday morning.
The sea crossing between north Africa and southern Spain is increasingly favoured by migrants, according to the International Organization for Migration (IOM).
So far in 2018, Spain has been the second most popular entry point for incomers to Europe. IOM figures say some 1,279 arrived there, while 4,256 went to Italy.
Not including those recovered this weekend, 243 migrants have already died or gone missing this year after trying to cross the Mediterranean.