Sweden reinstated border controls on Thursday in a bid to gain control over the massive influx of migrants arriving in the country, without blocking the steady flow of asylum seekers.
On Thursday at 12:00 pm (1100 GMT), police began carrying out identification checks on passengers travelling on trains crossing the bridge over the Oresund strait from Denmark, an AFP correspondent reported.
Police were also checking papers at terminals for ferries arriving in southern Sweden from Denmark and Germany.
Those are the routes most used by migrants.
"This is not a fence. We need to make sure that we have control ... We have to make sure we know who is coming to Sweden," Prime Minister Stefan Lofven insisted.
"Introducing border controls is not to prevent people from coming to Sweden to seek asylum," the head of the Swedish Migration Agency, Anders Danielsson, meanwhile told Swedish news agency TT.
"On the contrary. They will have their case heard, but we need to (regain) control," he added.
Sweden, a country of 9.8 million people, has taken more refugees as a proportion of its population than any other country in Europe, as the continent struggles with its worst migration crisis since World War II.
The Scandinavian country expects to receive up to 190,000 asylum seekers this year -- the equivalent of 1.5 million people arriving in a country the size of Germany, and more than double the 80,000 it took in last year.
The massive influx has strained Sweden's capacity to take care of the new arrivals, with authorities recently warning they were no longer able to provide housing for them.
"People are forced to sleep in tents, in offices and in evacuation centers" normally used for natural disasters, Migration Agency spokesman Mikael Hvinlund said.
"We are not fulfilling our mission, which is to offer a roof to everyone... Re-establishing border controls can help us," he said.
People arriving in Sweden without valid identification documents would be allowed to seek asylum, but those who do not want to do so -- for example those who simply want to transit through Sweden -- would be refused entry.
'Children are disappearing every day'
Police spokeswoman Ewa-Gun Westford said the border checks would require a large police presence.
"We will try to be on all trains, at least to start with, and then we will have to make an assessment... We are in a situation today where we assess this operation hour by hour," she said.
The decision to reinstate border checks is temporary and valid for 10 days but can be renewed for up to six months under Schengen regulations on free movement.
Swedish police officials said Thursday they were preparing to have the controls in place for six months, though Sweden has made no such request yet.
Authorities have also expressed concern about the large number of unaccompanied minors arriving in the country -- 23,000 have arrived so far this year, a sharp rise from previous years.
"We don't have control over the unaccompanied minors," Hvinlund said.
"Children are disappearing every day now, it's not acceptable," he said.
Sweden, long known for its generous asylum policy and welfare state, last week asked Brussels to relocate to other EU countries some of the asylum seekers it has taken in.
And earlier this week, two polls indicated Swedes wanted their government to start taking in fewer migrants.
With the Swedish welfare system subjected to gradual cuts over the past 25 years, the strain the influx is putting on Sweden is challenging the generous "Swedish model".
That has spurred anti-immigrant rhetoric and rising support for the far-right Sweden Democrats in opinion polls.
Sweden's ruling Social Democrats "are worried about losing voters to the anti-immigration Sweden Democrats, who were capitalising on people's fears over mass migration to Sweden," said Magnus Hagevi, political scientist at Linnea University.
"Already we've witnessed a rash of arson attacks on migrant facilities across Sweden -- people are also worried about the price of immigration. Many people are worried about what the future will bring and how that will affect the welfare state," he said.