ZAGREB (AFP) - Croatia on Saturday announced an unprecedented spike in the arrival of migrants on a long, dangerous journey towards western Europe as the continent's worst post-World War II refugee crisis showed no sign of abating.

With many of the people fleeing war and misery flocking towards Germany, a new poll showed Chancellor Angela Merkel's popularity at home has been hit by her policy of openness.

Merkel's "strong commitment to the refugees has obviously not been met with much backing," the Der Spiegel weekly newspaper said on the poll published Saturday on its pages.

Germany is expecting up to a million refugees and migrants to enter its borders this year, many encouraged by Merkel's welcoming stance.

Some 500,000 people have come to Europe so far this year, the International Organisation for Migration says, many of them taking perilous journeys on inflatable dinghies to Greece from Turkey, and then up towards western Europe through the Balkans and Hungary.

EU member Croatia became a key transit country when Hungary sealed its border with Serbia earlier this month in a bid to keep the migrants out.

In the past 10 days alone, 65,000 refugees and migrants have arrived in the Balkan country, the interior ministry said Saturday.

Most were given temporary shelter in a recently-built refugee reception centre in the village of Opatovac near the Serbian border. They were then taken on buses and trains to three border crossings with Hungary.

"The key is that everything goes smoothly on Hungary's side. (Hungary) is still receiving (the migrants) and transporting" them on towards the Austrian border, Interior Minister Ranko Ostojic told reporters.

"The situation is under control," he added.

However, with hardline Hungary planning to seal the border with Croatia too, there is speculation that people might carve out a new so-called southern route through Montenegro.

Ostojic said preparations were under way in southern Croatia in case the need to give them shelter arises there.

Croatia may temporarily house them in military facilities remaining from the former Yugoslav People's Army in the Prevlaka peninsula, which is located at southern tip of Croatia's long coastline on the Adriatic Sea, 45km south-east of Dubrovnik, bordering Montenegro.

Some regional officials have warned however that Croatia must prevent any influx of migrants near the resort of Dubrovnik as it might affect tourism.

MERKEL SEEKS UNITY

Merkel, with her popularity down over her handling of the crisis, on Saturday sought to bring back the spirit of the country's reunification in 1990, to help face today's challenge of integrating the refugees.

While admitting that handling the current wave of migration and facing the task of reunification are two very different things, Merkel said integrating people will require a similarly important effort from the whole of German society.

"That general feeling - when we are faced with a major task that we can achieve - that, I believe, we can absolutely remember how to do," Merkel said in her weekly podcast.

Their memory of the reunification process of east and west Germany is what has encouraged "many, many people to get involved today... Their approach to their task is with the idea that 'we want to succeed, and we can succeed.'"

More than 250,000 people claimed asylum in Germany from January to July this year, among them 55,587 people who said they were Syrian.

BULGARIA CHURCH FEARS 'INVASION'

The European Union's enlargement commissioner, meanwhile, warned in an interview with the German Die Welt newspaper that the next wave of migration could come from Syria's tiny neighbour, fragile Lebanon.

"Developments in Lebanon unsettle me. The situation there is... dramatic," Johannes Hahn told the conservative-leaning daily.

EU leaders have agreed to boost aid for Syria's neighbours, including US$1 billion (S$1.4 billion) through UN agencies, in a bid to mitigate the refugee influx into Europe.

EU interiors ministers recently pushed through a deal to relocate 120,000 refugees amid fierce opposition from central and eastern states.

But resistance to welcoming the migrants remains strong in hardline states, with the Bulgarian Orthodox Church on Saturday calling on the government not to let any more Muslim refugees into the country to prevent an "invasion".

The EU member has largely been bypassed by the refugees, most of whom set off from Greece through neighbouring Macedonia and Serbia.

The migration crisis has sparked concern in some quarters, playing into the hands of the far-right across Europe which hopes to turn fears of migrants into electoral success.