Thousands of migrants again streamed into the Balkans Monday where tighter border controls caused tense bottlenecks, as Germany braced for anger at an anniversary rally of the anti-refugee PEGIDA movement.

Europe's unprecedented influx has seen asylum seekers -- mainly fleeing war in Syria, Iraq and Afghanistan -- travelling via Turkey, Greece and the western Balkans, hoping to seek safe haven in Germany and other EU states.

Tensions have built along the migrant trail after Hungary shut its key borders with razor wire -- diverting the flow west to Slovenia, which in turn also limited arrivals, as did Croatia.

On Monday, thousands of refugees waited in cold and heavy rain at one of the chokepoints, Berkasovo on the Serbia-Croatia frontier, where families huddled around fires and children walked barefoot in the mud.

"This is beyond our capacity," said Czech volunteer Jan Pinos. "There is no one from the authorities here. We need police, army, some tents, food."

He warned of "increasing tension" and desperation among pregnant women and children, including a baby that nearly died overnight in the chaos.

"It's a matter of time before this is out of control," Pinos told AFP as more continued to arrive on foot or in taxis and buses.

Despite the delays, there has was no sign of a let-up.

More than 15,000 crossed from Greece into Macedonia at the weekend, said local authorities. From there, the UN refugee office said, 10,000 marched on into Serbia overnight.

By the agency's count, more than 600,000 migrants have come to Europe's shores so far this year, on dangerous journeys that have left more than 3,000 dead or missing.

The ultimate goal for many is the EU's biggest economy, Germany, which expects to take in around one million refugees this year, and where Chancellor Angela Merkel's open-door policy has sparked a dangerous backlash.

'Hate in their hearts'

Two days after a man with a neo-Nazi background stabbed a pro-refugee politician in the neck, badly wounding her, Germany's anti-refugee PEGIDA movement was planning a mass rally to mark its first anniversary.

Police expected thousands to join the "Patriotic Europeans Against the Islamisation of the Occident" demonstration in Dresden in the former communist East, as well as a large antifascist counter-protest, from 1600 GMT.

The movement had all but vanished after pictures surfaced in January showing its co-founder Lutz Bachmann sporting a Hitler moustache, but it has made a comeback since September, when Merkel opened the doors to a surge of asylum seekers.

Angry protesters have accused her of "treason" and last week carried a mock gallows with Merkel's name on it.

The chancellor on Monday again urged people to "stay away from those with hate in their hearts," her spokesman said.

Interior Minister Thomas de Maiziere said PEGIDA's organisers were "hardcore right-wing extremists" and implored citizens to "stay away from those who inject this hate, this poison into our country".

Anti-foreigner sentiment motivated a bloody attack in the western city of Cologne on Saturday when a 44-year-old man used a hunting knife to stab independent mayoral candidate Henriette Reker, 58, who has been active in helping refugees.

Reker, who was seriously wounded in the neck, went on to win Sunday's election with an absolute majority.

De Maiziere said the attack had left him "speechless" and also pointed to a tripling of attacks against asylum seekers from last year that had left more than 40 people injured.

Tension has also flared into violence inside some crowded migrant shelters.

In Hamburg, an 18-year-old Afghan man was hospitalised with head wounds after a mass brawl involving 40 to 50 people overnight. Police arrested two Eritreans and one Iranian man.

More fences?

The migrant influx has boosted support for populist right-wing parties in other European countries, including Austria.

A Swiss populist party known for its virulent campaigns against immigration, the EU and Islam won a record number of seats in parliamentary elections on Sunday.

In Germany, Merkel has faced a dip in opinion polls and a rebellion in her own conservative ranks, especially in the southern state of Bavaria, the main gateway for migrants.

While the Bavarian CSU party wants to establish "transit zones" along the Austrian border to hold and register asylum seekers, a police union chief has called for a fence to secure the Alpine frontier.

A group of 188 of the 310 lawmakers in Merkel's conservative block has doubts about her refugee policy, and its chairman Christian von Stetten said considering "border fortifications" must "not be taboo", according to Bild daily.

Merkel, hoping for Turkey's help in slowing the migrant influx, held talks with President Recep Tayyip Erdogan in Istanbul on Sunday.

The EU wants Turkey to tighten border security and house more refugees in return for billions in financial help, visa liberalisation for Turkish citizens and an acceleration of its stuttering drive for EU membership.

But Turkish Prime Minister Ahmet Davutoglu said on Monday his country would not host migrants permanently to appease the EU.

"We cannot accept an understanding like 'give us the money and they stay in Turkey'," he said. "Turkey is not a concentration camp."

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