Scores of migrants broke through a police line near a refugee center on Monday and marched against oncoming traffic on a motorway hard shoulder headed for Budapest.
Europe's borders are near breaking point as authorities struggle to cope with influx of people fleeing war and poverty in the Middle East and Africa, with thousands making their way across the Balkans and the Mediterranean every day.
Meanwhile, fresh clashes erupted between police and migrants on the Greek island of Lesbos Monday night, which authorities said was "on the verge of explosion," as Britain and France pledged to accept tens of thousands more refugees from the record influx.
Lesbos, home to some 85,000 people which has seen more than 15,000 mainly Syrian migrants wash up on its shores, is one of several Greek islands struggling to cope with a wave of voyagers setting sail from the nearby Turkish coast for Western Europe.