Danish Prime Minister Lars Lokke Rasmussen made the announcement on Monday, just hours after Sweden's decision to step up its own border controls came into effect.

The border controls are temporary, according to Rasmussen, although it's not clear how long they will be in place.

Earlier on Monday, Sweden announced it was implementing a new system of ID checks for train passengers crossing into Sweden from Denmark as it tries to cope with the influx of migrants. Travelers will be required to show identification as they pass across a bridge-and-tunnel transit area linking Copenhagen Airport to Sweden.

A further blow to Schengen?

Denmark and others criticized that move, calling it a blow to the open borders Europe has long touted as one of its defining traits. Shortly after the announcement was made, German Foreign Ministry spokesperson Martin Schäfer said the Schengen zone was "in danger," according to AFP news agency.

"Freedom of movement is an important principle - one of the biggest achievements in recent years," Schäfer told reporters.

The move has also drawn backlash from ordinary citizens in both countries, with the head of the Commuters Association, the organization that represents those who make the daily commute across the border, telling that some are even referring to the border as "the new Iron Curtain."

A Danish man who currently lives in Sweden told DW he was even considering moving back to his native country after the decision. "We have kids to pick up after school and shopping to do. How's that going to work, if it all takes an hour extra?"

Sweden has the highest number of asylum seekers in Europe after Germany. Some 160,000 people applied for asylum in Sweden last year, most of them from Syria, Iraq and Afghanistan.

blc/se (AP, AFP, dpa)