Refugees stuck in long lines Sunday at the Serbia-Croatia border urged one another to "be patient" as thousands of people waited restlessly for hours. Meanwhile, officials in neighboring Slovenia and Austria put restrictions on the number of refugees those countries would accept, further restraining the flow of asylum seekers into Europe.

Two Syrian sisters, Rawan and Dina, held up a makeshift sign calling for calm on the Serbian side of the border, Agence France-Presse reported. "There are no buses right now. Be patient, we will tell you when to go," read the message written in Arabic, scrawled across a pink rubber board.

The sisters had traveled to Serbia from war-torn Damascus with their father. The family was among the roughly 2,000 refugees waiting to cross into Croatia Sunday afternoon as officials tightened the flow of travelers, AFP said.

"Everything has slowed down since Hungary closed the border," a police officer at the Berkasovo crossing in Serbia told AFP. Hungarian officials blocked the border with Croatia Friday night after European Union leaders failed to agree on a plan to stem the flow of asylum seekers. The police officer said it took Croatian buses longer to reach Slovenia and back than it did to Hungary.

Hungary Refugees A group of migrants cross the border before Hungarian soldiers closed the border between Hungary and Croatia in Zakany, Oct. 16, 2015. Photo: Attila Kisbenedek/AFP/Getty Images)

The border closing is putting pressure on Croatia, Slovenia and Austria to accept more asylum seekers. Croatian officials Sunday called on Slovenia for relief, urging the neighboring nation to take 5,000 people a day. Slovenia said it would allow just 2,500 people to cross its borders daily, citing a bottleneck at the tiny nation's border with Austria.

Austrian officials, for their part, notified Slovenia late Sunday it could not take any more refugees from Slovenia for the time being, Austria's Interior Ministry said in a statement cited by the Slovenian Press Agency.

More than a half-million refugees have arrived in the EU since January amid escalating conflicts in North Africa and the Middle East. Nearly 60 percent of all asylum seekers in Europe are from Syria where the 4 1/2-year civil war has killed hundreds of thousands of people and displaced 7 million, the United Nations has estimated.