Men and women trying to enter Spain without documents stand inside a Spanish Civil Guard boat after they were intercepted in Tarifa, southern Spain.
The United Nations refugee agency says a record number of migrants this year have made the sometimes deadly crossing of the Mediterranean to Europe and calls the increase "alarming."
A statement on Thursday said 165,000 people have made the crossing this year, compared to 60,000 for all of last year.
Concerns have soared as migrants largely from Africa and the Middle East risk their lives in growing numbers. The refugee agency says at least 3,000 people have died so far this year.
UNHCR says more people are fleeing war or persecution, with people from Syria and Eritrea making up almost half of the crossings since July 1.
It demands more help for rescues at sea, saying, "If Europe fails in these efforts, many more lives will continue to be lost."