Migrants wait at the train station in Tovarnik, Croatia, September 17, 2015. Amid chaotic scenes at its border with Serbia, Croatia said on Thursday it could not cope with a flood of migrants seeking a new route into the EU after Hungary kept them out by erecting a fence and using tear gas and water cannon against them. [Photo/Agencies]

The Croatian police said on Thursday it banned all traffic on roads leading to seven border crossings with Serbia.

"The measure is valid until further notice," police said in a statement.

The traffic ban includes the border crossing of Tovarnik, near where most migrants entered Croatia from Serbia over the last two days. Police said 11,003 migrants have entered Croatia since Wednesday morning, driven from trying to enter through Hungary by a metal fence, tear gas and water cannon.

Interior Minister Ranko Ostojic said earlier on Thursday that Croatia would close its border with Serbia if the inflow of migrants again hits 8,000 people a day. He also said that Croatia had no capacity to receive new migrants.

Amid desperate scenes at a railway station on Croatia's eastern frontier, where thousands were left stranded overnight under open skies, the European Union called an emergency summit next week to try to overcome disarray in the 28-nation bloc.

Croatia said it may have to use the army to stop thousands of migrants criss-crossing the Western Balkans in their quest for sanctuary in the wealthy 28-nation bloc. It shuttled some to reception centres near Zagreb, but many simply slipped the net of overwhelmed authorities and set off for the Slovenian border, just 30 kilometres (19 miles) from the Croatian capital.

There, Slovenian police halted a train carrying some 150 migrants at Dobova train station on Slovenia's side of the border and said they would be sent back. A Reuters TV crew said some tried to leave the train but were stopped by police. Some refused water in protest.

Slovenia later stopped all train traffic on the main line from Croatia through the border point and police stepped up checks in the area with helicopter and land patrols.

"We will return them (the migrants) to Croatia in the shortest time possible," Anton Stubljar, a local police official, told reporters.

The stalled train threatens to become the latest symbol of an EU deeply divided over how to handle the influx of hundreds of thousands of people mostly fleeing war and poverty in Syria, Iraq, Afghanistan and Pakistan.

Croatian Interior Minister Ranko Ostojic said the country would close its border with Serbia if another 8,000 were to pour over the border in one day.

Macedonia tried a similar tactic last month ago, lobbing tear gas and stun grenades to keep back crowds, but was eventually overwhelmed. Hungary did it with a 3.5-metre (10-foot) fence built the length of its frontier with Serbia and a raft of immigration laws that rights groups say break international law.

Hungary's crackdown has shifted pressure onto Croatia, Slovenia and Romania.

At the eastern border town of Tovarnik, scuffles broke out as Croatian police tried to get women and children to board the buses bound for reception centres near Zagreb. Women screamed and children cried in desperate scenes.

An Iraqi from Baghdad who gave his name as Riad said he had been separated from his wife and child. "Only women and children are now allowed onto buses. My wife and child are gone and they (police) do not allow me to join them. My phone does not work."

Groups of migrants broke away from the police and set off on foot down railway lines and through fields.

"They want to take us to the camps, but we don't want that," said one man as he set off, without giving his name.