By Johan Ahlander and Maja Zuvela

STOCKHOLM/LJUBLJANA (Reuters) - Sweden said on Thursday it expected up to 190,000 migrants this year, putting unprecedented strain on a country famous for welcoming refugees but planning to house many in tents this winter.

At the opposite pole of the angry debate on the migration crisis, Hungarian Prime Minister Viktor Orban urged European leaders to change their immigration policies and consult voters, or face a threat to the democratic order.

Thousands of refugees continued to pour into Slovenia in the hope of reaching prosperous northern Europe, and the tiny country appealed for other European Union states to send police to help manage the flow.

Europe is struggling to cope with its biggest wave of migrants since World War Two. According to the International Organization for Migration, more than 670,000 people have arrived by sea this year, fleeing war zones and poverty in the Middle East, Africa and Asia.

Sweden's Migration Agency said more than 30,000 of the 140-190,000 people it expected in 2015 would be unaccompanied children. Such numbers are much higher, as a proportion of Sweden's population of under 10 million, than even the 800,000-plus expected by Germany.

"We have seen pictures of people who are literally walking from Greece across the Balkans to Germany and on to Sweden," agency head Anders Danielsson told reporters.

The agency said it would need an additional 70 billion Swedish crowns ($8.41 billion) over the next two years to cope.

More than 100,000 have already arrived in Sweden this year, topping the previous record during the Balkan wars in the early 1990s.

Nearly 10,000 came in the past week alone.

"Last night all our places were full," Danielsson said.

The Agency estimated it would face a shortage of accommodation for 25,000-45,000 migrants by the end of the year. Tens of thousands could spend the cold Swedish winter in heated tents.

ATTACKS

Polls show most Swedes still welcome refugees, but there have been attacks on asylum centers. The anti-immigrant Sweden Democrats party is set to launch an advertising campaign in foreign media to discourage people from coming.

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Polls give the party around 20 percent support, up from 13 percent in the last election in autumn 2014.

German police warned on Thursday of a growing threat of attacks on politicians by radicals angry about an influx of migrants, and said crimes directed at refugee shelters were increasing dramatically.

Slovenia has asked the European Union for police to help regulate the inflow from Croatia, Interior Minister Vesna Gyorkos Znidar said.

Since last Friday, when Hungary sealed off its border with Croatia, migrants from Syria, Afghanistan and other strife-torn countries have instead started entering Slovenia, which like Hungary is a member of the EU's Schengen visa-free zone.

Slovenia said more than 12,000 migrants had crossed into its territory in the last 24 hours. Bottlenecks are forcing thousands to sleep outdoors in Serbia, Croatia and Slovenia.

Anas Kaial, from Hama in Syria, spent the night under open skies with his mother, wife and three children.

"It was so cold," he said after arriving in Slovenia from Croatia. "The only way we could distract our children from the cold and make them stop crying was by telling them that they will get all the Barbie dolls they want once we come to Germany."

TALKING STRAIGHT

Hungary has fortified its borders against the tide of migrants and spoken of a threat to Europe's Christian and democratic way of life.

Orban told the state television channel m1 that European leaders had no mandate to let hundreds of thousands in.

"This destabilizes European democracies," he said. "We need to start the debate about the future of our continent honestly, without the muzzle of 'political correctness', without pretence, talking straight."

U.N. human rights chief Zeid Ra'ad al-Hussein said on Thursday the Czech Republic was committing systematic human rights violations by detaining refugees for up to 90 days and strip-searching them for money to pay for their own detention.

He said he was alarmed by Islamophobic statements by Czech President Milos Zeman, and concerned about the conditions in detention facilities. Children were also detained, which was unjustifiable, he said.

Prague rejected the criticism and Interior Minister Milan Chovanec said he wanted the U.N. official to visit to see detention facilities for himself. Few migrants claim asylum in the Czech Republic and many head for Germany upon release.

"The president has long warned of the threat of Islamic fundamentalism. He stands by his opinion and he will not change it under pressure from abroad," Zeman's spokesman said.

Zeman has warned Muslim immigrants will impose sharia law. "We will lose women's beauty because they will be covered head to toe in burqas," the CTK news agency quoted him as saying last week.

A study said the five million foreigners living in Italy paid for the pensions of 620,000 people. European Central Bank President Mario Draghi said separately the influx of migrants was "a very significant increase in labor supply" for Europe but it was too early to tell what the effect would be.

British support for staying in the European Union has tumbled over the past four months, partly because of the migrant crisis, pollster Ipsos MORI said.

Turkish President Tayyip Erdogan said there were signs of a new wave of migration following an increase in fighting in the Syrian region of Aleppo.

Seven members of a Lebanese family who died trying to reach Greece by boat were buried on Thursday in Beirut.

"There is not a Lebanese citizen who does not know the circumstances that led to this," said a cousin of one victim. "The country has driven people to risk their lives and migrate."

(Additional reporting by Marja Novak, Marton Dunai, Laila Bassam, Tom Miles and Jan Lopatka; Editing by Andrew Roche and Catherine Evans)