By Marja Novak and Maja Zuvela

LJUBLJANA/DOBOVA, Slovenia (Reuters) - Slovenia said it will consider all options, including fencing off its border with Croatia, if European leaders fail to agree a common approach to the migrant crisis as thousands stream into the ex-Yugoslav republic.

Migrants began crossing into Slovenia last Saturday after Hungary closed its border with Croatia. The Slovenian Interior Ministry said that a total of 50,400 had entered the country since Saturday, and some 10,300 are at the moment in the tiny country.

"We can not receive so many refugees in such a small period of time..It's just unbearable," Prime Minister Miro Cerar told reporters outside a refugee camp in Dobova.

Late on Thursday evening when asked if there was the possibility of building a fence on the border, Cerar told Slovenian state TV: "We are considering also those options."

Several European leaders are due to meet in Brussels on Sunday under the auspices of the European Commission to discuss the latest developments in the migrant crisis, Europe's biggest since World War.

Hundreds of thousands of people fleeing war and poverty in the Middle East, Asia and Africa have reached Europe this year, with hundreds losing their lives in risky voyages across the Mediterranean.

Most are trying to reach Germany and other rich countries.

Croatia began directing migrants into Slovenia, which is part of the European Union's open border Schengen Area, after Hungary closed its borders.

But bottlenecks have built up along new routes and border crossing points in the Balkans, and aid workers fear the humanitarian crisis will deepen as winter weather sets in.

Slovenia has asked for the EU for assistance and officials said Austria, Germany, Italy, France, Hungary, the Czech Republic, Slovakia and Poland offered to send police reinforcements.

'I WANT THIS TO COME TO AN END'

A Reuters cameraman said about 3,000 people broke the fence at the border crossing at Sentilj and walked in to Austria on Friday morning.

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Larisa, 30, from the Syrian town of Aleppo held her arms her nine-month old son from as she waited in a field outside the small town of Rigonce, near the border crossing with Croatia, to be escorted to the camp. From the camp she will go to Austria.

"I can't put my baby away even for a second. It's cold and he can't stop crying," she said. "I only want this to come to an end."

On Friday, Serbian Interior Minister and his Croatian counterpart agreed to speed up the transit of refugees from Serbia to Croatia. Trains will be taking migrants four times a day from the Serbian town of Sid, straight to the Croatian town of Slavonski Brod, where a new camp will be open within days.

At the moment refugees walk through orchards from Serbia in to Croatia and thousands get stuck in no man's land overnight as temperatures approach freezing levels.

"We have agreed to stop this torture due to cold and everything else," Croatian Interior Minister Ranko Ostojic said.

In Austria, a police spokesman in Styria province said a few thousand people had crossed into Austria from Slovenia on Friday morning.

"Some people are walking on train tracks and roads, causing traffic disruptions. Several hundred people had to sleep outdoors last night," he said.

(Writing by Ivana Sekularac, Additional reporting by Aleksandar Vasovic and Shadia Nasralla in Vienna, Editing by Angus MacSwan)