Austria's new daily cap on asylum seekers has entered into force, in a move that the European Commission has described as "plainly incompatible" with European Union laws.
Since 7am Irish time, a maximum of 80 migrants per day are being allowed to claim asylum in the country, police said.
In addition, Vienna is limiting the daily number of people transiting Austria to seek asylum in a neighbouring country to 3,200.
Once the quotas have been reached, "the borders will be closed," a police spokesman said.
He added that due to bad weather, no migrant had arrived at the Austrian-Slovenian frontier since yesterday afternoon.
Vienna's measures - announced earlier this week along with tougher controls at 12 checkpoints along its southern borders - drew an angry reaction from the EU yesterday
"Such a policy would be plainly incompatible with Austria's obligations under European and international law," European migration commissioner Dimitris Avramopoulos complained in a letter to Austrian Interior Minister Johanna Mikl-Leitner.
European Commission President Jean-Claude Juncker also criticised the proposal.
"As far as Austria is concerned I have to say I don't like this decision, we are questioning whether it is within European law, and we will have a friendly discussion," Mr Juncker told a news conference.
Meanwhile, Austria's interior minister told reporters at a conference on migration that Austria has received around 11,000 asylum claims so far in 2016, putting it on course under the new daily limit to exceed its ceiling for the year of 37,500.
Last year, Austria accepted 90,000 asylum seekers, making it one of the EU's highest recipients on a per-capita basis.
As a result of the number of asylum claims so far, the interior minister said Austria "will have to reduce these upper limits even further".
She added that the daily cap on claims only applied to people arriving at the southern border on the main migrant route into Europe.
Earlier, Austrian Chancellor Werner Faymann said there "will be no lifting of the decision," speaking at a two-day EU summit.
Vienna says that the measures are necessary because a German-backed EU plan for Turkey to stem the flow of migrants setting off from its coast is not yet working, and has urged other countries on the Balkans route into Europe to follow suit.
In response, Slovenia, Croatia and Serbia have also tightened their borders.
In 2015, over one million people reached Europe's shores - nearly half of them Syrians fleeing a civil war that has claimed more than 260,000 lives.
The vast majority enter the EU through Italy and Greece, where they should register, but poor controls mean most are able to continue their journeys to northern Europe.
