At least 300 people traveling in three boats from Senegal to Spain are missing, a Spanish aid group said Monday, raising concern about their fate along one of the deadliest sea routes for migrants.

Two boats departed from Mbour city on June 23 carrying about 100 people and a third left the southern town of Kafountine four days later with approximately 200 people, said Helena Maleno Garzon, coordinator for Walking Borders (Caminando Fronteras). “The most important thing is to find those people. There are many people missing in the sea, this isn’t normal, we need more planes to look for them,” she said.