Germany has started checks at borders with five more European countries in an effort to crack down on “irregular” migration and guard against Islamist threats.
Police are now checking vehicles at the land frontier with France, Denmark, the Netherlands, Belgium and Luxembourg.
The checks are due to last six months and follow similar inspections, in place since last year, at the Polish, Czech, Austrian and Swiss borders.
Germany announced the expanded system last week.
It follows the deaths by stabbing of three people in the city of Solingen last month – an attack blamed on a Syrian asylum seeker said to share the ideology of Islamic State.
A police officer was also killed by a failed Afghan asylum seeker in Mannheim in May.
The incidents sparked renewed debate around migration and in the aftermath of the Solingen attack the far-right Alternative for Germany party won a regional election.
Germany’s restrictions are contrary to one of the EU’s key principles – free movement without border checks between member countries.
However, states are allowed to temporarily reintroduce them as a last resort, and for a limited time, if there is deemed to be a serious security threat.
Police – some carrying large firearms – were seen checking vehicles as the restrictions began on Monday, but traffic seemed to still be flowing freely.
Germany’s interior ministry said the new controls would be “targeted”, rather than applied to everyone, and applied flexibly, based on the latest security situation.
People are being advised to carry identification and non-EU citizens should have visas and entry documents to hand.
Interior minister Nancy Faeser said the system was “intended to protect against the acute threat of Islamist extremist terrorism and serious cross-border crime”.
She said the first set of border restrictions had stopped 52,000 people gaining unauthorised entry to Germany and that asylum applications had dropped by a fifth.
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The checks have caused concern among some of Germany’s neighbours, who fear a negative effect on trade and having to take in more asylum seekers.
Polish Prime Minister Donald Tusk is seeking urgent discussions with other countries affected by the measures.
Austria’s chancellor has also said that if Germany sends more immigrants back across their border it will direct more people east toward the Balkans.
The checks with Austria are due to end on 11 November, while those affecting Poland, Switzerland and Czech Republic are slated to end in December.
However, Germany’s interior ministry has implied that an extension is likely.