Austria announced on Monday it would dispatch the armed forces to guard its southern frontier, following Germany's lead in re-imposing Europe's internal border controls after thousands of migrants streamed across its frontier from Hungary on foot.
Austrian officials said they were left with no choice after Germany's decision on Sunday, which effectively suspends Europe's two-decade old Schengen regime allowing border-free travel across the continent.
"If Germany carries out border controls, Austria must put strengthened border controls in place," Vice Chancellor Reinhold Mitterlehner told a joint news conference with Chancellor Werner Faymann. "We are doing that now."
He and Mr. Faymann said the army would be deployed in a supporting role.
"The focus of the support is on humanitarian help," Mr. Faymann said. "But it is also, and I would like to emphasise this, on supporting border controls where it is necessary."
Before the announcement, migrants were walking across the border from Hungary at the fastest rate yet. Police said they were running out of emergency accommodation, including tented camps near the border and the car parks of railway stations.
An Austrian police spokesman said that by mid-morning, 6,000 to 7,000 people had arrived since midnight, after 14,000 on Sunday.
The European Union has been struggling to cope with the unprecedented arrival of hundreds of thousands of migrants, many refugees fleeing war in the Middle East. Nearly all arrive at the bloc's southern and eastern edges and head over land to seek asylum in richer states further north and west.
The Schengen system, established in 1995, removes all border checks between 26 European states, but the rules still bar undocumented migrants from travelling. Countries are permitted to re-impose border checks temporarily in emergencies.
Illegal travel across internal Schengen borders by migrants has become a major issue in recent weeks, especially after Berlin suspended normal EU asylum policy to announce it would take Syrian refugees who arrive elsewhere in the European Union.
Austria has served as the main conduit for refugees heading to Germany from the EU's land border in Hungary. It suspended its rail link to Hungary last week because of what the national rail company called a "massive overburdening" of its network.
Germany and Austria acted in unison more than a week ago to lift restrictions on the entrance of migrants from Hungary. But Berlin's decision on Sunday to reverse course appeared to catch the Austrian government by surprise. At a hastily convened news conference on Sunday night, Mr. Faymann and Mr. Mitterlehner had given no clear indication as to whether Austria would reintroduce checks.
"The accommodation centres in Nickelsdorf, Parndorf, and in the near surroundings are all full," the police spokesman said, referring to the area near the border crossing where almost all migrants have arrived from Hungary recently.
"At the moment, no buses are running," he said. "The only buses that are running are taking people to the station until a special train leaves, but otherwise we have no accommodation at the moment."
A train service was running to Vienna, and buses had taken people to other parts of the country overnight, the police spokesman said, adding that the number of people entering south of the main crossing point was growing.
At Heiligenkreuz, where until recently only dozens of migrants had crossed each day, arrivals had reached 1,000 to 2,000 on Sunday, in addition to those counted at the main crossing, he said. More were expected on Monday.
