SOFIA (AFP) - Bulgaria, Romania and Serbia on Saturday (Oct 24) threatened to close their borders if EU countries stopped accepting migrants, as European leaders prepared for a mini-summit on the continent's worst refugee crisis since World War II.

Bulgarian Prime Minister Boyko Borisov said the three countries wanted a Europe-wide solution to the crisis but were not prepared to become a "buffer zone" for the tens of thousands of new arrivals.

The Bulgarian, Romanian and Serbian premiers held talks in Sofia on the eve of a meeting called by European Commission chief Jean-Claude Juncker, who has been urging a cross-border approach to the crisis, which has seen 670,000 people arrive on Europe's shores this year.

The influx has prompted EU member Hungary to close its borders with Serbia and Croatia to halt the flow of new arrivals, and Slovenia has threatened to do likewise.

Mr Borisov and his Serbian and Romanian counterparts said the best solution was commonly-agreed action across Europe, but warned that if other EU countries followed Hungary's lead, they would have to act.

"All three countries, we are ready if Germany and Austria and other countries close their borders (...) we will be ready to also close our borders at that very same moment," Mr Borisov said after the talks with his Romanian and Serbian counterparts.

"We will not let our nations become a buffer zone of the migrant flows that will become stranded between Turkey and the fences built up from Serbia."

Over past months non-EU member Serbia has been swamped by migrants on their way from Greece and Macedonia to northern Europe, though Bulgaria and Romania have so far largely remained on the sidelines of the influx.

Hostillity towards new arrivals has been growing in Germany and Sweden, Europe's most sought-after destinations for asylum seekers, lending increased urgency to efforts to get other EU members to accept a greater share of the arrivals.

Police in Sweden said a planned refugee home, around 90km west of Stockholm, was torched on Friday night in a suspected arson attack.

The building was vacant at the time but there have been a dozen such attacks since the start of the year. On Thursday (Oct 22), a man armed with a sword killed two people in a racist attack at a Swedish school with many immigrant pupils.

Authorities in Germany have also reported mounting anti-migrant violence. On Thursday, prosecutors said police had foiled a far-right plot to torch migrant shelters in the southern town of Bamberg.

Germany, the EU's top economy, has taken in the vast majority of the migrants landing in Europe this year, most fleeing conflict in Syria, Iraq and Afghanistan.

On Saturday, a new German law came into effect to speed up the expulsion of people deemed to be economic migrants and to restrict political asylum for Albanian, Montenegrin and Kosovan nationals to exceptional cases.

Mr Juncker on Friday praised Chancellor Angela Merkel's policy of solidarity with refugees, which has drawn sharp criticism as the country braces for up to a million asylum requests this year.

But in a sign of possible fresh tension within the EU, the small Alpine country of Slovenia - a new hotspot in the crisis - warned it could add to the growing number of European anti-migrant border fences unless it received more support.

More than 47,500 people have entered the country of just two million since Oct 17 when Hungary shut its frontier with Croatia, barely a month after also closing its Serbian border.

Sunday's summit in Brussels will bring the leaders of non-EU members Macedonia and Serbia together with the leaders of eight EU countries: Austria, Bulgaria, Croatia, Germany, Greece, Hungary, Romania and Slovenia.

"The past weeks have shown that there is no national solution to the problem," Mr Juncker's spokesman Margaritis Schinas told reporters.

"Only a European collective cross-border approach based on cooperation can succeed."

According to German media, Mr Juncker has drafted 16 proposals for Sunday's talks, including an undertaking that no country will let migrants through to an adjoining state without first getting the neighbour's agreement.

He will reportedly also float proposals to speed up the expulsion of migrants who have been denied asylum and to withdraw the right of asylum to people who do not register their request in the first EU state where they land.

Asylum statistics published by Switzerland on Saturday showed it rejecting more and more asylum requests from Eritreans arriving via Italy, on the grounds that their request should be handled in their first port of call in the EU.