French Prime Minister Manuel Valls urged the Hungarian government to treat migrants at its borders humanely, saying its current attitude toward them was unacceptable.

"We are shocked by the images of women at Europe's borders. Each migrant must be treated with respect and humanely. We can not accept the statements, nor the attitudes, nor the barbed wire," Valls told reporters in Stockholm.

Germany on Friday criticized Hungary's border closures to migrants, saying they do "not contribute to a sustainable solution" to the refugee crisis.

Berlin "is aware of the great challenges" faced by transit countries including Greece, Macedonia, Serbia, Hungary and Croatia, said Chancellor Angela Merkel's spokesman Steffen Seibert.

Hungarian troops overnight began laying a razor-wire barrier along its border with Croatia to keep migrants out, Prime Minister Viktor Orban said Friday, following a similar move along the frontier with Serbia.

"During the night work already began on building the technical border closure... It seems we can rely on help from no-one," Orban said in an interview on public radio after thousands of migrants entered Croatia seeking to travel to northern Europe.

Hungarian Foreign Minister Peter Szijjarto on Thursday slammed as "shocking" criticism of the police's use of tear gas and water cannon during clashes with migrants at the Hungary-Serbia border.

Angrily brushing off criticism, including from U.N. chief Ban Ki-moon who said such treatment of refugees and migrants was "not acceptable," Szijjarto defended the police's actions at a press conference in Budapest.

The European Parliament on Thursday backed plans to relocate 120,000 refugees around the EU to help the frontline states of Greece, Hungary and Italy, in a move that raised pressure on ministers to adopt the proposals next week.

In an emergency vote called after EU interior ministers failed to back the scheme on Monday, lawmakers approved the plans by the European Commission -- the EU's executive -- by 372 votes to 124 with 54 abstentions.

Dozens of migrants on Wednesday managed to break through Hungarian police lines on the Serbian border and force their way into Hungary at the flashpoint Roszke crossing, AFP correspondents said.

After an hour of clashes, the crowds managed to pull down wire meshing across two access routes to Hungarian territory, with riot police moving back some 50 meters (yards) then firing tear gas at them.

Hundreds of migrants who had massed at the main train station in the Austrian city of Salzburg left on foot Wednesday in the hope of reaching Germany, a city spokesman said.

One day after Salzburg warned that the station might have to close due to the large numbers of migrants, government spokesman Johannes Greifeneder said the situation had "relaxed".

Only 367 migrants crossed illegally into Hungary on Tuesday, the first day of tough laws to punish unauthorized entry into the country, and all were arrested, police said Wednesday.

Of the total, 316 will be prosecuted for damaging a barbed-wire fence set down by Hungary on its Serbian border, and the other 51 for illegally entering the country, they said. 

Several dozen migrants entered Croatia from Serbia early Wednesday, the first to enter the EU country after Hungary sealed its borders to thousand of people entering every day, an AFP correspondent saw.

The group of mostly Syrian or Afghan men, women and children crossed the border -- which was marked by nothing more than a stone -- early Wednesday morning and were picked up by police as they walked across a field.

Hungary sealed its border with Serbia on Tuesday to stem the massive influx of refugees as Germany slammed the "disgraceful" refusal of other EU countries to accept more migrants after 22 died in yet another shipwreck.

Budapest's move came after Austria and Slovakian authorities followed Germany's lead in reimposing border controls, a further body blow to Europe's cherished passport-free Schengen zone as the EU's border agency said more than half a million migrants had been counted at the bloc's borders so far this year.