Hungarian police have fired tear gas and water cannon at protesting refugees who are demanding entry from Serbia.
The move on Wednesday came after "the crowd on the Serbian side became aggressive and threw stones, bottles and sticks at police on the Hungarian side and crossed the barrier at the border", Hungarian police said.
Later in the day, Hungary said it had detained 29 refugees during clashes at the border.
"Police also captured an identified terrorist," Gyorgy Bakondi, a security adviser to Hungarian Prime Minister Viktor Orban, said in an interview with the country's state television M1.
Al Jazeera's Mohammed Jamjoom, reporting from the Serbian side of the border in Horgos village, said that the refugees were angry for being "detained" at the border on their way to their final destination - Germany.
"Hungarians are standing strong on their pledge to not allow refugees into Hungary. They have now criminalised illegal crossings into Hungary and we suspect that's the reason why they deployed the water cannons," Jamjoom said.
Meanwhile, the first refugees crossed the Serbia-Croatian frontier on Wednesday, carving out a new route through Europe after Hungary sealed its borders.
Croatian police on Wednesday said they were registering refugees entering from Serbia and would transport them to reception centres near the capital Zagreb.
READ MORE: Hungary enforces tough new immigration law
A police spokesman in the eastern border county of Vukovarsko-Srijemska confirmed an unspecified number of refugees had crossed into Croatia, after a Reuters news agency cameraman saw at least 100 walking through fields across the border.
Earlier on Wednesday, a group of 30-40 mostly Syrian or Afghan nationals arrived at the Serbian town of Sid near the Croatian border. They had travelled by bus from the Macedonian border at Presevo, 500km to the south.
The new route takes the refugees to Croatia, from where they will have to travel through Slovenia to get to northern Europe.
Until this week, the vast majority of refugees travelled up from Greece, through Macedonia and Serbia into Hungary.
Earlier on Tuesday, Hungary declared a state of emergency, and shut its border with Serbia leaving many desperate refugees stranded at the border.
Orban has indicated that asylum requests from refugees trying to enter Hungary from Serbia will be rejected, because Serbia is a safe country where refugees do not risk war or persecution.
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Slovakia has also started spot-checks at its borders with Hungary and Austria , fearing it could be a new transit point for refugees.
Austria imposed new restrictions at its borders on Tuesday, as it struggled to cope with a backlog of thousands trying to reach Germany.
The AP news agency also reported that the temporary control imposed by Austria from midnight local time (22:00 GMT) on the Hungarian border may also be extended to other nations.
Thousands of refugees have poured into Austria in recent days, rushing through Hungary ahead of a deadline that saw that country close its border with Serbia.
Merkel on Tuesday called for a special EU refugee summit, urging unity after an angry reaction to a suggestion by one of her ministers that countries that did not take in their share of asylum seekers could face financial penalties.
The proposal by Interior Minister Thomas de Maiziere was forcefully rejected by the Czech Republic and Slovakia, which are among Eastern European states that have resisted EU plans to share out refugees.
Merkel later took a more conciliatory tone, calling for Europe to come together on the refugee issue.
"I think we need to establish a European spirit again... I don't think threats are the right way to achieve agreement," she told a news conference with Austrian Chancellor Werner Faymann, whose country is also in the front-line of the refugee crisis.
Facing opposition from ex-communist states, EU ministers failed on Monday to break a deadlock over sharing responsibility for accepting some of the hundreds of thousands who have sought asylum in Europe.
They have been summoned back to Brussels next Tuesday but diplomats said those calling for national refugee quotas were loath to simply outvote their eastern neighbours.
De Maiziere said an agreement was still some way off.
Source: Al Jazeera And Agencies