Chancellor Angela Merkel's dramatic reinstatement of checks on Germany's frontiers marked a new phase in the continent's migrant crisis and struck at the heart of the EU's cherished Schengen agreement, which allows border-free travel throughout most of the bloc.
"Europe's inaction in the refugee crisis had driven Germany... To the limit of its capacity," her deputy Sigmar Gabriel told the Tagesspiegel daily.
Underscoring the scale of the challenge, Hungarian authorities said Monday they had registered a record 5,809 migrants streaming into the country the day before, amid reports that neighbouring Serbia might try to "push through" as many as 30,000 people before draconian new laws come into force.
Barely five minutes after Germany reinstated the border controls, police halted three young migrants fleeing war in Syria, asking to see their passports.
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"We have been walking through Europe for 22 days," said 27-year-old Hatem Ali Ahaj, who suffers from asthma and was struggling to catch his breath.
"We thought that Germany was the only country that would treat us like human beings," he said.
Facing the biggest refugee crisis since World War II, ministers from EU member states will gather later today in Brussels to try and heal deep divisions in the bloc over migrant policy.
But the abrupt U-turn and admission that even powerhouse Germany cannot cope with the record influx has underlined the importance of interior ministers' talks in Brussels later today.
The European Commission - the EU's executive - last week unveiled a plan to redistribute 160,000 migrants across the continent to relieve pressure on "frontline" states such as Italy, Greece and Hungary.
However, this has run into stiff opposition from several Eastern European states such as the Czech Republic and Slovakia.