Migrants onboard a drifting overcrowded wooden boat react during a rescue operation by the Spanish NGO Proactiva Open Arms, north of the Libyan city of Sabratha in central Mediterranean Sea, March 29, 2017. REUTERS/Yannis Behrakis TPX IMAGES OF THE DAY - RTX3387O

A migrant is helped by Proactive Open Arms rescuer to board a RHIB during a search and rescue operation north of the Libyan city of Sabratha in central Mediterranean Sea, March 29, 2017. REUTERS/Yannis Behrakis - RTX33893

Spanish NGO Proactiva Open Arms rescuers ferry migrants in their RHIB as hundreds of migrants are seen overcrowding a wooden vessel drifting in central Mediterranean Sea off the Libyan coast, March 29, 2017 during a search and rescue operation. REUTERS/Yannis Behrakis - RTX338YN

A search and rescue Spanish air force aircraft flies overhead an overcrowded wooden vessel drifting in central Mediterranean Sea off the Libyan coast, March 29, 2017 during a search and rescue operation by Spanish NGO Proactiva Open Arms. REUTERS/Yannis Behrakis - RTX338Q7

A migrant onboard a drifting overcrowded wooden boat reacts during a rescue operation by the Spanish NGO Proactiva Open Arms, north of the Libyan city of Sabratha in central Mediterranean Sea, March 29, 2017. REUTERS/Yannis Behrakis TPX IMAGES OF THE DAY - RTX3389U

Migrants overcrowding a wooden vessel call for help to rescuers from the Spansh NGO proactiva Open Arms in central Mediterranean Sea off the Libyan coast, March 29, 2017 during a search and rescue operation. REUTERS/Yannis Behrakis - RTX3393S

Migrants overcrowding a wooden vessel call for help to rescuers from the Spanish NGO Proactiva Open Arms in the central Mediterranean Sea off the Libyan coast, March 29, 2017 during a search and rescue operation. REUTERS/Yannis Behrakis TPX IMAGES OF THE DAY - RTX338TC

Migrants onboard a drifting overcrowded wooden boat react during a rescue operation by the Spanish NGO Proactiva Open Arms, north of the Libyan city of Sabratha in central Mediterranean Sea, March 29, 2017. REUTERS/Yannis Behrakis - RTX3386F

Over 400 migrants are seen overcrowding a wooden vessel drifting in central Mediterranean Sea off the Libyan coast, March 29, 2017 during a search and rescue operation by Spanish NGO Proactiva Open Arms. REUTERS/Yannis Behrakis - RTX338Q8

Migrants are seen onboard a drifting overcrowded wooden boat, during a rescue operation by the Spanish NGO Proactiva Open Arms, north of the Libyan city of Sabratha in central Mediterranean Sea, March 29, 2017. REUTERS/Yannis Behrakis - RTX3388V

Spanish NGO Proactiva Open Arms rescuers help a migrant to board their RHIB as hundreds of migrants are seen overcrowding a wooden vessel drifting in central Mediterranean Sea off the Libyan coast, March 29, 2017 during a search and rescue operation. REUTERS/Yannis Behrakis - RTX338Q4

Migrants onboard a drifting overcrowded wooden boat react during a rescue operation by the Spanish NGO Proactiva Open Arms, north of the Libyan city of Sabratha in central Mediterranean Sea, March 29, 2017. REUTERS/Yannis Behrakis - RTX3386H

Kalifa Kujabi, 17, from Gambia, is helped by Proactive Open Arms rescuer to board a RHIB during a search and rescue operation north of the Libyan city of Sabratha in central Mediterranean Sea, March 29, 2017. Kalifa an amateur soccer player in Gambia is trying to reach Germany and become a professional soccer player. REUTERS/Yannis Behrakis - RTX3388R

Migrants overcrowd a wooden vessel during a rescue operation by the Spansh NGO proactiva Open Arms in central Mediterranean Sea off the Libyan coast, March 29, 2017. REUTERS/Yannis Behrakis - RTX3393C

Spanish NGO Proactiva Open Arms rescuers help migrants as hundreds of migrants are seen overcrowding a wooden vessel drifting in central Mediterranean Sea off the Libyan coast, March 29, 2017 during a search and rescue operation. REUTERS/Yannis Behrakis TPX IMAGES OF THE DAY - RTX338RI