Germany confirmed Tuesday it has stopped returning Syrian asylum-seekers to their first port of entry in the EU, an action hailed as "European solidarity" as thousands more migrants pour into the bloc seeking refuge.

Record numbers of migrants are streaming into EU member Hungary from Serbia, posing a new headache for regional leaders at a summit this week set to be dominated by Europe's worst migrant crisis since World War II.

As criticism mount over the bloc's failure to find a response to tackle the crisis, Germany said it has waived a key EU procedure regarding asylum claims for Syrians, becoming the first country in the bloc to effectively simplify the process for those fleeing the war-torn country.

"For the commission, this constitutes a recognition of the fact that we cannot leave the member states at the external borders alone in dealing with a large number of asylum seekers seeking refuge in Europe," said Natasha Bertaud, spokeswoman for the EU Commission.

Under the so-called Dublin rules, the first EU country that an asylum-seeker arrives in is required to process the claimant's application.

In practice, this means that countries on the EU's borders like Greece or Italy are overwhelmed with applications as thousands arrive by sea on their shores.

Hungary, another EU country with external borders, is rushing to build a vast razor-wire barrier to keep out migrants, fearing that it would be overwhelmed by asylum requests.

Almost 2,100 people, the highest ever daily total, crossed into Hungary near the town of Rozko, one of the few sections of the border not yet sealed off by the barrier.

They were among 7,000 refugees whose hazardous journey to the European Union was temporarily blocked last week when Macedonia declared a state of emergency and shut its borders for three days to halt the huge influx of people mostly fleeing war in Syria.

Authorities reopened the crossing after chaotic scenes involving police lobbing stun grenades at migrants trying to break through the border.

"We were stopped in Macedonia for two days, the riots were terrible, police used guns and teargas, I saw an old woman beaten, her money and papers taken," said a 29-year-old IT engineer from Mosul in Iraq who said he had left his home to escape the Islamic State group. He asked not to be named.

The UN's refugee agency said on Tuesday it expected the number of refugees moving through Macedonia to double from around 1,500 per day to 3,000 per day, many of them women and children.

It warned that the situation was also worsening on the shores of Greece and Italy, where the number of Mediterranean sea crossings was now approaching 300,000.

Since the beginning of the year, more than 2,370 have drowned in the Mediterranean, already exceeding the death toll for the whole of 2014, according to the International Organization for Migration.

The UN called on Europe to "establish a human-rights based, coherent and comprehensive migration policy", as the bloc struggles to agree a response to the unprecedented numbers of refugees arriving -- from the thousands landing on the shores of Greece and Italy to the hundreds risking their lives to climb onto trucks to travel from France to Britain.

"Let's not pretend that what the EU and its member states are doing is working," said the UN's special rapporteur on the human rights of migrants, Francois Crepeau.

He called for "opening up the regular labor markets through smart visas" to be issued to migrants.

His comments came as Britain announced tough new measures against illegal migrant workers, with those caught working without permits in England and Wales facing up to six months in prison.

The migration crisis is set to dominate the summit in Vienna of leaders from the western Balkans region on Thursday that will also be attended by German Chancellor Angela Merkel, whose country expects to take in 800,000 migrants this year, a record number.

The passage via the western Balkans has now become one of the main ways into the EU for the several hundreds of thousands of migrants entering the bloc this year.

More than 1,700 migrants were massed Tuesday in Serbia's Miratovac camp, waiting for an opportunity to cross into Hungary.

Yet, while many are fleeing war, nearly half of those arriving in Germany come from conflict-free Balkan states such as Kosovo and Albania. Merkel wants to use the summit to find out why "so many thousands of people are coming from these countries", her spokesman Steffen Seibert said.

Some 102,000 migrants arrived in the EU via Macedonia, Serbia, Bosnia and Herzegovina, Albania, Montenegro or Kosovo between January and July this year, versus just 8,000 for the same period in 2014, according to EU border agency Frontex.

Summit host Austria, which borders Hungary and fellow "front line" state Italy, will put forward a five-point plan at the conference.

It involves doing more to tackle people-trafficking gangs, a "fairer" distribution of refugees around the EU, greater security cooperation, helping the countries where the migrants come from and a "pan-European asylum strategy".

"There is a pressing need for us to focus on the situation in the western Balkans," Austrian Foreign Minister Sebastian Kurz said earlier.

His office confirmed that Hungary would not be involved in the conference, but did not specify why.