Hungarian Police Fire Tear Gas at Migrants. Officials say migrants throwing stones and bottles broke through newly closed border crossing.

“These are not peaceful migrants,” Foreign Minister Peter Szijjarto said. “This is aggressive mass migration.”

Hungarian Police Fire Tear Gas at Migrants

Officials say migrants throwing stones and bottles broke through newly closed border crossing

By MARGIT FEHER and

MATT MOFFETT

Updated Sept. 16, 2015 1:17 p.m. ET / http://www.wsj.com/articles/migrants-look-for-new-routes-after-hungary-crackdown-1442401929?mod=e2fb

BUDAPEST—Violence erupted on Hungary’s southern border as riot police used tear gas and a water cannon to force back migrants who had breached a razor-wire fence, as the clampdown along its frontier pushed others to switch to a potentially more dangerous route through Croatia.

For most of Wednesday, the Hungarian government’s move to seal off its 110-mile border with Serbia with a newly erected fence seemed to have largely succeeded in keeping out migrants trying to enter the European Union via Hungary. Thousands of people, camped in tents or curled up in sleeping bags, hunkered down in northern Serbia.

But near the Hungarian town of Roszke—a major transit point for migrants following the so-called West Balkan route from Turkey and Greece into Western Europe—a small group of tired and impatient refugees revolted, seeking to swarm the fence and throwing stones at the police who tried to repel them with tear gas and water cannons. Hungary said it would apply a new law that went into effect on Tuesday making illegal border crossings a criminal offense punishable by up to three years in jail.

Hungarian Foreign Minister Peter Szijjarto called upon Serbia on Wednesday afternoon to act immediately and stop the migrants on the Serbian side of the border from attacking the Hungarian police guarding the frontier.

Scores of migrants crossed into Croatia from Serbia overnight on Wednesday. Meanwhile, many migrants have been camping on the Serbian side of the border with Hungary, as breaches in the newly erected Hungarian fence continued to be made.

Hungary’s tough tactics have made Croatia—which like its neighbor Hungary, is part of the EU and shares a border with Serbia—a new front line in Europe’s migration crisis. But the alternate route through Croatia and Slovenia onto Austria, is longer than the way through Hungary—and fraught with new risks. Croatia’s border region with Serbia remains peppered with land mines going back to the Balkan conflicts of the 1990s.

In contrast to Hungary, Croatia’s government said it was willing to assist the refugees, who are mainly coming from war-torn parts of the Middle East and Afghanistan, in their trek to more affluent countries in Western and Northern Europe.

“We are ready to accept and direct those people, regardless of their religion or the color of their skin,” Croation Prime Minister Zoran Milanovic said. “Fences that are being erected will not stop anyone and they are only sending a terrible and dangerous message.”

But the alternate route through Croatia and Slovenia onto Austria, is longer than the way through Hungary—and fraught with new risks. Croatia’s border region with Serbia remains peppered with land mines going back to the Balkan conflicts of the 1990s.

About 370 migrants had crossed the border from Serbia into Croatia by Wednesday afternoon, the Croatian Interior Ministry said. Privately operated buses in Serbia have been taking arriving migrants from Presevo, on Serbia’s border with Macedonia, to Sid, a five-hour drive away on the Serbian side of the border with Croatia, Serbian and Hungarian media reported. Some 2,500 migrants traveling through Macedonia had arrived in Presevo during the night and another 1,500 in the morning.

The European Commission, the EU’s executive arm, held talks about the newly forming migrant routes. “Any attempt to build walls and fences is not the Europe we want,” said EU trade commissioner Cecilia Malmstroem who briefed journalists about the meeting. “Desperate people who run away from war and dictatorship will try to seek alternative routes.”

She repeated calls for EU governments next Tuesday to endorse a plan to redistribute across the bloc 120,000 people seeking asylum. “We really hope member states share this urgency and that there will be an agreement next week,” she said.

The government of Hungarian Prime Minister Viktor Orban has defended its decision to construct the border fence and remained steadfast in its argument that Germany’s openness to refugees is encouraging the continued flow.

After the confrontation between police and migrants on Wednesday, Hungary said it would close both of its border crossings at the village of Roszke for the next 30 days. “These are not peaceful migrants,” Foreign Minister Peter Szijjarto said. “This is aggressive mass migration.”

Hungarian authorities said Wednesday they had arrested 367 migrants for illegal border crossing. Migrants submitted 94 asylum requests at two Hungarian transit zones, police said on Wednesday, most of which were likely to be rejected because Hungary holds that migrants should be required to stay where they first entered the EU, which for most of them is Greece.

The impact of Mr. Orban’s crackdown could also be seen downstream on Hungary’s northern border with Austria, where the stream of refugees had virtually halted. “Close to no migrants have crossed the Hungarian-Austrian border today,” said a police spokesman for the Austrian border region of Burgenland.

Meanwhile at the end of the route in Germany, migrants continued to flow from Austria, despite Berlin introducing document checks at its border, slowing down the stream and disrupting traffic.

Unlike last week, authorities are now registering migrants at the border and dispatching them directly across Germany’s 16 states, relieving the pressure on Munich, which had so far acted as the main reception hub for trains full of migrants on their way from Vienna.

In Austria, chaos momentarily erupted when Austria’s rail operator earlier Wednesday halted traffic between Munich and Salzburg, leaving hundreds stranded at the town’s train station. A spokeswoman for German rail operator Deutsche Bahn also said traffic between the two cities was heavily disrupted Wednesday as police stopped trains to take migrants to local police stations for registrations.

—Martin M. Sobczyk in Warsaw and Ruth Bender in Berlin contributed to this article.

Write to Martin M. Sobczyk at martin.sobczyk@wsj.com and Margit Feher at margit.feher@wsj.com