Hundreds of thousands of migrants are entering Europe via little-known "covert" routes increasingly used since some nations adopted stricter border controls, a think-tank said on Friday.
Some 330,000 migrants are expected to arrive in the EU through the well-known Mediterranean routes this year, but the number of asylum applications is forecast to reach 890,000, the Overseas Development Agency said.
The difference of more than 500,000 "shows that there are many people whose journeys to Europe we know little about," the ODI said.
"These refugees and migrants travel to Europe through a variety of ‘covert’ channels and means: some over land concealed in vehicles; others by plane with false documents or by overstaying visas," it said.
Only about one-third of these migrants are from Syria, it said, with most from middle-income countries.
The ODI said European governments should "shift from an emphasis on controlling and deterring migration, towards a pragmatic and effective approach to manage it better."
It urged European governments to increase cooperation and develop more "legal pathways so that they can monitor and more effectively manage flows of refugees and migrants."
"Deterrence measures and border controls are expensive and mostly ineffective," the ODI warned.
"Border controls have, in many cases, simply rerouted refugees and migrants towards alternative, 'covert' routes," it said.
It said some 1.1 million people arrived in Europe by sea and 1.7 million people applied for asylum last year, but numbers have fallen following an EU–Turkey deal and other bilateral agreements on migrants.