European Union justice and interior ministers started urgent discussions Monday on how to tackle the refugee crisis amid the stream of new arrivals and continuing disagreements over how to seal off borders.

The informal meeting comes days after EU president Donald Tusk warned that Europe's passport-free travel area, known as Schengen, could break apart if the migrant strategy is not sorted out within two months.

"In order to maintain and ensure the free movement within the Schengen zone, it is obvious that we have to better manage our external borders," said the EU's migration commissioner, Dimitris Avramopoulos.

Ministers are seeking to stem the flow through Greece, where authorities are struggling to contain the crossings by boat from Turkey. If that fails, Europe may need to set up border controls somewhere else, Austrian Interior Minister Johanna Mikl-Leitner said.

"It's clear that if we can't secure the European borders — that means the Greek-Turkish border — then the Schengen border will move to central Europe," she told reporters.

EU figures show more than 2,000 people are still arriving daily, despite choppy seas and wintery conditions.

Italy's Interior Minister, Angelino Alfano, said his country was not in favour of effectively pushing Europe's border up to Greece's northern border with Macedonia.

"We are of the idea that Europe must remain a stable structure, that there cannot be bits of Europe inside and bits of Europe outside because that would be the start of dissolution," he said.

Ministers arriving for the meeting at Amsterdam's Maritime Museum were met by protesters in two boats, one full of showroom dummies wearing red life vests similar to those worn by migrants crossing from Turkey and another with a large sign saying: "Leaders of Europe, it's not the polls you should worry about. It's the history books."