The move came after Germany imposed controls on its border with Austria.
EU states are struggling to cope with a steady stream of arrivals, many aiming for Germany where the vice-chancellor said one million may arrive this year.
European interior ministers are to hold an emergency meeting on the migrant crisis later on Monday.
They are due to vote on a plan from May to redistribute an initial 40,000 asylum seekers from Syria and Eritrea through mandatory quotas, though Central and East European states have opposed this.
The EU has since raised the total number of people it seeks to share out through quotas to 160,000 asylum seekers across 23 EU states.
Also on the agenda is a plan to agree a common list of countries considered safe for migrants to be sent back to - a measure that could speed up deportations.
Meanwhile, the EU approved a plan for its operation in the Mediterranean to conduct "boarding, search, seizure and diversion of vessels suspected of being used for human smuggling or trafficking".
Europe is experiencing an enormous influx of people, mostly from Syria but also Afghanistan, Eritrea and other countries, fleeing violence and poverty.
Many migrants have been refusing to register in countries such as Greece or Hungary, fearing it will stop them being granted asylum in Germany or other EU states.
