Migrants, including minors, who arrived swimming at the Spanish enclave of Ceuta, rest as Spanish soldiers stand guard on May 18, 2021 in Ceuta. (AFP)
The latest discoveries bring to eight the number of bodies found after a boat carrying migrants that had been spotted west of Spain's Cape Trafalgar sank on Thursday.
"During the course of the day today, four bodies have been found," said a coastguard spokesman.
The vessel was first spotted around 70 kilometres (40 miles) off Cape Trafalgar by a passing merchant ship which sounded the alarm, and rescue teams were mobilised overnight Thursday to Friday.
Two men were found alive on board the boat while a woman was rescued from the water. The survivors said the boat had departed for Spain with 28 people on board.
It is not clear what nationalities were on the boat or from where on the north African coast they set off.
Helicopters and several vessels scoured the waters Friday and Saturday but found no more survivors. The coastguard statement said the search would resume on Sunday.
This kind of operation is fairly common off Spain's southern coast, which is a target for migrants trying to make the dangerous crossing from the coast of north Africa, mainly from Morocco or Algeria.
Migrant boats are tempted in part by the narrowness of the Strait of Gibraltar, a 13-kilometre (eight-mile) wide waterway that separates Europe and Africa, despite strong currents that sink many boats.
More than 27,000 migrants arrived by sea in continental Spain and the Balearic and Canary Islands between January and the end of September, a 54 percent increase over the same period in 2020, according interior ministry figures.
The International Organization for Migration says at least 1,025 migrants have died trying to reach Spain in 2021, making it the "deadliest year" on the migratory route.