
With the route through Hungary apparently closed, some migrants set out on a longer, more arduous route into Western Europe through Croatia.
Frustrated migrants - many of them war refugees from Syria and Iraq - who were blocked on the Serbian side of the border threw plastic water bottles and rocks at helmeted riot police and chanted demands that the now-sealed border be re-opened.
One of those who fainted was a woman who was holding a baby. Children and women cried while young men with scarves over their faces hurled stones as they charged toward the police through thick tear gas smoke. Several Serbian ambulances arrived to treat the injured.
The crowd also lit up old tires, causing dark smoke to fill the air. Hungarian media reported that a pregnant woman began giving birth to a baby amid the clashes.
Government spokesman Zoltan Kovacs described the group as an "armed mob of illegal migrants," telling reporters at the border that "these people are using kids as a human shield."
Hungary's Foreign Minister Peter Szijjarto decried what he called "brutal attacks" by the migrants against Hungarian police and asked Serbia authorities to crack down on the migrants, who were on the Serbian side of the border.
Serbian Labor and Social Care Minister Aleksandar Vulin expressed "the harshest possible protest" over Hungary's use of tear gas and water cannons against the people at the border. Speaking on Serbian state TV from the Horgos border crossing, Vulin said he urged refugees to go to a migrant center in Kanjiza to get food, water, medical aid and rest for a while.
He didn't have any information about the injured, but said incidents were expected as Hungary closed the border. "Hungary must show it is ready and capable to accept these people," said Vulin.
Hungarian authorities also said that they have arrested a total of 519 migrants who tried to cross the border since tough new laws went into effect on Wednesday that make it a crime to cross from Serbia anywhere other than at legal checkpoints. Authorities launched 46 criminal prosecutions and found two Iraqi men guilty, the first convictions based on the new laws.
Two men were expelled from Hungary and banned from re-entering the country for a year.
Syrian President Bashar Assad blamed Europe for the crisis, saying it's a direct result of the West's support for extremists in Syria over the past four years.
In an interview with Russian media, Assad accused Europe of supporting "terrorism" and providing "protection for terrorists, calling them moderates."
Earlier in the day, Hungary's foreign minister denied that closed borders and tough new laws signal callousness toward refugees, repeating the government's claim that most of those entering Hungary are actually economic migrants.
"Based on our history, we are always in solidarity with the refugees," Szijjarto told The Associated Press in an interview. "What we're saying is that we cannot accept economic migrants because we cannot bear the burden of that."
Migrants trapped at border crossing near Horgos, a Serbian village, were confused about whether to keep waiting or to try to enter the EU through Croatia, a longer and less direct path into Western Europe.
"I don't know what to do - stay here or try some other way to cross the border," said Ahmed Sami from Aleppo, Syria. "We walked and traveled for hundreds, thousands of kilometers only to be stopped meters from the European Union. My wife and children cannot stand on their feet any more. This is tragic."
At least 300 crossed into Tovarnik, Croatia, after they were bused to the Serbian border town of Sid on an all-night ride from Macedonia.
Croatian Prime Minister Zoran Milanovic criticised Hungary's decision to seal its border with Serbia for migrants and said Croatia will not do the same.
"We are ready to accept these people, regardless of their religion and the color of their skin, and direct them to the destinations where they wish to go, Germany and Scandinavia," Milanovic told lawmakers in Parliament.
Elsewhere in Europe migrants remained on the move.
Greek police said about 5,000 refugees and migrants crossed the country's northern border with Macedonia in the 24 hours from Tuesday morning to Wednesday morning.
Meanwhile, Austria began selective controls of vehicles at three main border crossings with Hungary as it tries to impose some order over the stream of people.