Spanish sea rescue services said, four African migrants drowned and up to 35 have been missing after their boat sank in the Mediterranean in the early hours of Thursday about 40 miles (65 km) north of the Moroccan coast.
Earlier, 15 people including two women were rescued from the boat after it lost its bottom and sank. They were found clinging to the wreckage, sea rescue services said.
According to a sea rescue spokesman's statement, lifeguards pulled four bodies from the sea after they were spotted by a Colombian military helicopter helping in the search.
One of those rescued said there had been 54 people in the boat.
The operation continues to find any survivors and bodies. The survivors have been taken to the southern Spanish city of Malaga.
Although refugee numbers decreased after Spain have taken tighter security measures, The Mediterranean between Morocco and Spain is still one of the major route for refugees from Africa who try to reach Europe.
According to a report released by the International Organization for Migration in September, 2600 refugees died trying to cross the sea to reach Europe in overcrowded boats.
The International Organization for Migration said more than 350,000 refugees have crossed the Mediterranean this year, far exceeding last year's number, which was 219,000 for the entire year of 2014. An estimated 234,778 people have made it to Greece and 114,276 people made it to Italy, while 2166 debarked in Spain and 94 arrived in Malta.