BRUSSELS: Bitterly-divided European leaders will seek to find a credible response to the continent's worst migration crisis since World War Two at an emergency summit this week.

German chancellor Angela Merkel called on her peers on Sunday to accept joint responsibility. "Germany is willing to help. But it is not just a German challenge, but one for all of Europe," Merkel told a gathering of trade unionists. "Europe must act together and take on responsibility. Germany can't shoulder this task alone."

Striking a more sceptical tone on migration than in previous weeks, Merkel also warned that Germany could not shelter those who were moving for economic reasons rather than to flee war or persecution.

"We are a big country. We are a strong country. But to make out as if we alone can solve all the social problems of the world would not be realistic," she told a gathering of the Verdi trade union.

European Council President Donald Tusk, who chairs European Union summits, said on Twitter on Sunday following a weekend visit to Jordan and Egypt that the EU needed to help Syrian refugees find a better life closer at home.

That will be one of the topics of discussion for Wednesday's summit in Brussels as hundreds of thousands of refugees and migrants brave the seas and trek across the impoverished Balkan peninsula to reach more affluent countries in northern Europe.

The 28-member bloc has struggled to find a unified response to the crisis, which has tested many of its newer members in the East that are unaccustomed to large-scale immigration.

On Sunday Hungary erected a steel gate and fence posts at a border crossing with Croatia, the EU's newest member state. Overwhelmed by an influx of some 25,000 migrants this week, Croatia has been sending them north by bus and train to Hungary, which has waved them on to Austria.

Around 10,700 migrants walked into Austria from Hungary on Sunday, some 200 more than on Saturday. 

The influx of migrants, most of them fleeing war and poverty in the Middle East, Africa and Asia, has led to bitter recriminations between European governments while the temporary closure of national borders has undermined one of the most tangible achievements of the Union.

"If you don’t cope with this crisis, then I think the EU will fall apart," said a senior EU official.

The official said European leaders would discuss longer-term strategies for dealing with the crisis, particularly increasing cooperation with Turkey and the countries bordering Syria to keep the millions of refugees at home. Tusk said more aid to the World Food Programme and the United Nations High Commissioner for Refugees would also be on the agenda.

Beefing up the EU's asylum agency, Frontex, into a full border and coastguard agency, and working on hotspots and a list of "safe countries" whose citizens would not normally qualify for asylum, would also be up for discussion, the official said.