Even Sweden has its limits.

A self-proclaimed "humanitarian superpower" where welcoming those fleeing war and oppression is ingrained as part of the national identity, the Nordic country has proudly taken in more refugees per capita than any other in Europe.

But now, with military barracks, ski lodges and camping huts already filling up, it is running out of roofs to put over the heads of immigrants. The government is warning that tens of thousands of people may end up spending the Nordic winter in tents.

And for the first time, there have been signs in recent weeks that the national consensus behind the open-door policy is crumbling. Far-right protesters have shouted "go home" at asylum seekers. Refugee housing has been hit by arson attacks. And even in the political mainstream there is a growing feeling that its generous policies are unsustainable.

Related reading Facebook page created to welcome refugees and migrants to Australia

With fewer than 10 million people, Sweden has already received 100,000 refugees so far this year, and the government now predicts 150,000 could arrive by year's end. That is more than double the number it expected when it set aside as much as four per cent of the 2016 state budget for immigration and integration.

Authorities will soon set up electrically heated tents that could house up to 35,000 people this winter, bringing to the cold dark reaches of northern Europe the sort of refugee camps more familiar in the poorest parts of the world.

"We are living from hand to mouth, and we have for a long time now," Tolle Furegard, national housing coordinator at the Migration Agency, told Reuters.

Early in the Syrian crisis, Sweden stepped out in front of other European countries to declare that all refugees from Syria would automatically be granted permanent residency, letting them work and making it easier for family members to join them.

Polls show most Swedes still welcome refugees, and several charities have received record donations. But a growing minority worry the influx will hurt their cherished welfare state.

Centre-left Prime Minister Stefan Lofven, heading a fragile minority government, faces calls from within his own Social Democrat party to tighten immigration - policies that over the decades welcomed refugees from Vietnam war draft dodgers in the 1960s to Gulf War refugees in the 1990s.

One municipality in northern Sweden is keeping the location of new homes for 150 refugees secret after three centres were torched. Another centre in western Sweden was forced to evacuate residents after it was set alight on Tuesday.

At Stockholm's train station, around 30 far-right demonstrators protesting what they see as an influx of Muslims to Sweden, gathered near a temporary migrations centre, shouting "Go home". The station, where volunteers help asylum seekers, has welcomed refugees for months.

Tent cities

"Sweden is preparing for a crisis situation," said Lofven, adding that asylum seekers will have to accept a lower standard of living. "It's about putting roofs over people's heads now."

Lofven's minority government faces a backlash from a centre-right and far-right opposition. The main centre-right Moderates, for years champions of immigration, now call for an end to granting permanent residency for asylum seekers.

In a country where questioning immigration was socially taboo a few years ago, several of the biggest newspapers are now criticising the government's policy.

The anti-immigration Sweden Democrats, the third biggest party in parliament, have risen further in polls, catching around a fifth of voters. They will start advertising in Middle Eastern media to deter people from coming to Sweden.

"Nobody should even think about coming here," said Paula Bieler, Sweden Democrats spokeswoman. "We have tented camps here. It's cold, chilly and snowy in Sweden. There is a shortage of resources both for our own population and for those who come here."

Lofven is diverting some foreign aid money back home to help meet the extra costs.

The government argues that investing money in improving integration for immigrants is crucial to staving off economic hardship in the future. But integrating newcomers has proved difficult. Unemployment among foreign-born Swedes is more than 20 per cent, four times higher than among natives.

"Integration has not worked as well as we would have liked," said Interior Minister Anders Ygeman. "It's clear that there are risks."

Adding to the cost is an unexpectedly high proportion of unaccompanied children among the refugees - a fifth of the total - requiring costly extra services.

Refugees first stop

The vastness of the enterprise can be seen at the main asylum centre in the southern city of Malmo where around two thirds of all asylum seekers to Sweden register.

The former hotel and conference centre is clean, with a restaurant and rooms for 600 people. The number of refugees arriving per day ballooned from 55 in July to around 900 in September. Staffing has doubled since the crisis started.

"I don't have to worry about the budget. My job is to make sure we don't close the door on anybody who comes here," said Patricio Mora, the centre's manager.

Lines quickly form outside and tempers flare when families jostle to enter.

Schools feel the strain. In Norberg, a community of around 5000 people about two hours drive from the capital, the 500-pupil school faces an extra 100 refugee students.

"We have used the library, storage rooms and the teachers lounge as classrooms. If even more children arrive in the coming weeks, we have nowhere to place them," said Asa Eriksson, the town mayor.

"If worst comes to worst they will have to be outside."