Migrants streaming across the Balkans reached Slovenia on Saturday, diverted overnight by the closure of Hungary's border with Croatia in the latest demonstration of Europe's disjointed response to the flow of people reaching its borders.

Hungary's right-wing government declared its southern frontier with Croatia off limits to migrants, blocking entry with a metal fence and razor wire, just as it did a month ago on its border with Serbia.

Croatia began directing migrants west to Slovenia, which said hundreds had arrived already and more were on their way.

Slovenia said they would be registered before continuing their journey to Austria and Germany, the preferred destination of the vast majority, many of them Syrians fleeing war.

But their movement had slowed visibly, with dozens of buses lined up at Serbia's border with Croatia through the night and into Saturday as Croatian police controlled their entry, a Reuters reporter said. Slovenia suspended rail traffic with Croatia, saying it needed "complete control" over the flow.

Aid agencies are concerned about backlogs of migrants building in the Balkans, battered by autumn winds and rain as temperatures drop before winter.

Hungary said it had reinstated border controls on its frontier with Slovenia, effectively suspending Europe's Schengen system of passport-free travel though it said it was acting within the Schengen rules. Both Slovenia and Hungary are part of the Schengen Area while Croatia is not.

A government spokesman said Budapest had taken the step because "migrants appeared" on the Slovenian side of the border.

Hungary says it is duty-bound to protect the borders of the European Union from the tide of migrants, most of them Muslims who Hungary says threaten the prosperity, security and "Christian values" of Europe.

With several other ex-Communist members of the EU, Hungary opposes a plan by the bloc to share out 120,000 refugees among its members. That is only a small proportion of the 700,000 migrants expected to reach Europe's shores by boat and dinghy from North Africa and Turkey this year, many of them fleeing war and poverty in the Middle East, Africa and Asia.


'Domino Effect'

Hungary dismissed as insufficient a proposal at an EU summit on Thursday to give Turkey 3 billion euros ($3.4 billion) in aid and the prospect of easier travel visas and "re-energised" talks on joining the bloc if it helps stem the flow of migrants across its territory.

Hungarian Prime Minister Viktor Orban, one of Europe's most vociferous opponents of immigration, wants the formation of a joint force to protect the borders of Greece, where most migrants arrive across the Aegean Sea from Turkey before heading north through Macedonia and Serbia. Without that, his government said it was left with no choice but to seal the border.

In Germany, a government official who declined to be named said the Hungarian border measures did little to solve the problem. "The measures run counter to our efforts to establish EU solidarity," the source said.

Slovenia, a small country of 2 million people, says it will allow in as many migrants as it is able to register and accommodate and put the army on standby to aid the effort.

"At the moment there are no problems and no need to use the army, but it is right to have such a plan if needed," Interior Ministry state secretary Bostjan Sefic told a news conference.

The first migrants of this new wave through Slovenia reached Austria on Saturday afternoon, police said. More were expected later in the day, with some 1,800 on board one train in Croatia that was due to stop at the Slovenian border.

Both Ljubljana and Zagreb say they will not restrict the flow so long as Austria and Germany keep their doors open. Otherwise, Croatian Interior Minister Ranko Ostojic warned of a "domino effect" of closed borders and migrant backlogs.

"It will be a lot of trouble for all countries and I cannot predict what will happen in this situation," Ostojic, speaking in English, told reporters at a migrant camp in the eastern Croatian village of Opatovac.

"They are risking their lives and nobody is able to stop this flow ... without shooting."

Despite rough seas, coastguards said migrants were still attempting the short but perilous crossing to Greece from Turkey, the main route for Syrian refugees embarking on their journey to northern Europe.

At least 16 migrants, including nine children, drowned in the Aegean Sea as they tried to reach Greek islands from Turkey, the Greek and Turkish coastguards said on Saturday, and more were missing.

In the Mediterranean, the Italian navy said it had rescued 562 migrants, all from sub-Saharan Africa, trying to reach Europe on five boats in difficulty in the Mediterranean on Saturday.