Germany has said the passport-free Schengen zone is “in danger” after both Denmark and Sweden introduced border controls to stem the flow of migrants.

Responding to the new border controls in the Nordic countries, German foreign ministry spokesman Martin Schaefer told reporters: "Freedom of movement is an important principle - one of the biggest achievements [in the European Union] in recent years….Schengen is very important but it is in danger.”

The concerns raised over the passport-free zone came as Denmark announced it would introduce controls at its border with Germany just hours after neighbouring Sweden introduced similar measures.

Danish prime minister Lars Løkke Rasmussen told reporters in Copenhagen that police were conducting spot checks on travellers crossing the border from Germany. Hours earlier Sweden imposed border controls on the Oresund bridge – which connects Malmo in southern Sweden and Copenhagen in Demark – making it harder for bother migrants and commuters to travel.

Mr Rasmussen, referring to the Swedish measure, said: “When other Nordic countries seal their borders it can have major consequences for Denmark… It can lead to more asylum seekers.” The Danish prime minister insisted, however, there would be no issues for “ordinary” Danes and Germans who wished to cross the border.

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He added: "If the European Union cannot protect the external border you will see more and more countries forced to introduce temporary border controls," the prime minister said.

The Swedish government decided to tighten border controls after 160,000 people applied for asylum in Sweden last year — the highest number in Europe except for Germany. Most of them were from Syria, Iraq and Afghanistan.