The number of migrants arriving in Spain by boat is surging, the United Nations migration agency said Tuesday, and it has now surpassed Italy as the top destination for Mediterranean crossings. The International Organization for Migration said that 50,872 migrants have crossed the Mediterranean to Europe so far this year-- less than half the number that made the treacherous journey during the same period of 2017, according to the UN migration agency. But while the overall numbers have fallen dramatically, Spain has seen landings on its shores nearly triple, IOM said. "As we have predicted for several weeks now, Spain has become the most active route of African migrants and people using Africa as a stepping stone into Europe," agency spokesman Joel Millman told reporters in Geneva. Spain "surpassed Italy this past weekend," he said. In all, 18,061 migrants have arrived in Spain since January, compared to 6,500 during the first half of 2017, with nearly 10,000 of those arrivals registered in June alone. At the same time, arrivals in Italy total 17,827 since the beginning of the year -- compared to 93,237 during the same period last year. Aid groups have reported a rise in the number of crossings to Spain and Greece compared to the previous year, while arrivals in Italy are down almost 80 percent from 2017. IOM says 1,443 people are dead or missing in the Mediterranean so far this year. The dramatic drop of Italian arrivals came after a controversial deal reached between Rome and the Libyan coastguard a year ago. The numbers have fallen further since Italys new populist government pushed the issue to the forefront of the EU agenda last month by refusing to open the countrys ports to a number of NGO migrant rescue ships operating in the Mediterranean. Spain has opened its ports to several rescue ships run by charities which were turned away from Italy.