Stockholm: Sweden's Migration Agency expects up to 190,000 refugees fleeing war in countries such as Syria and Iraq to arrive this year, putting strain on a country already planning to house thousands of asylum seekers in tents as the Nordic winter approaches.

The Migration Agency, which has often been forced to increase its estimates for refugee arrivals, gave a range of between 140,000 and 190,000 asylum seekers, of which 33,000 would be unaccompanied children.

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

"The current refugee situation is unprecedented both in a European and Swedish perspective."

The agency said it would need an additional 70 billion Swedish crowns ($8.41 billion) over the next two years to cope, based on a scenario where 160,000 refugees sought asylum in Sweden this year and another 135,000 next year.

It added the flow of asylum seekers was seen easing next year, but that the number could still reach as high as 170,000.

More than 100,000 asylum seekers have already arrived in Sweden this year, topping the previous record during the war in the Balkans in the early 1990s and surpassing the agency's July forecast for 74,000 for the whole of this year.

Nearly 10,000 asylum seekers arrived in just the past week, straining the country's ability to house the newcomers.

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

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

Polls show most Swedes still welcome refugees, but the influx of refugees has caused tensions.

There have been a number of attacks on asylum centers in the past week and the anti-immigrant Sweden Democrats party is set to launch an advertising campaign in foreign media to discourage asylum seekers from coming to the Nordic country.

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

The government and the main centre-right opposition parties are locked in negotiations over a broad agreement on how to deal with the record numbers expected this year. The Sweden Democrats are not part of the discussions