Hungary has confiscated a Croatian train that tried to transport 1,000 refugees into the country - describing its arrival as a breach of EU law.
The refugees were accompanied by 40 Croatian police officers, who were disarmed and sent back to their homeland in what Hungary called a "major, major incident". The driver was arrested.
Hungary said the refugees were being transferred to a reception camp.
Budapest has stated repeatedly that it will charge such refugees with illegal entry and expel them back to the country from which they arrived.
The train's seizure is the latest development in a spat between Croatia and Hungary which has left the fate of thousands of refugees uncertain.
Croatia's foreign minister, Vesna Pusic, said the countries had agreed "to provide a corridor", adding that "all these people want to go to Germany or northern Europe."
But Hungarian government spokesman Zoltan Kovacs said this was a "lie."
More than 4,000 refugees were sent from Croatia to Hungary on Friday after officials in Zagreb said the country did not have capacity to accommodate the 17,000 who had arrived since Wednesday.
In Hungary, Sky's Alex Crawford said it appeared bus loads of refugees were now being taken to registration camps on the Austrian border.
Others are being taken north towards the Slovakian border.
For its part, Austria, which sits between Hungary and Germany, said that if a corridor was being created, nobody had coordinated with its interior ministry.
Meanwhile, Ms Pusic also revealed that, of those who had been registered in Croatia so far, 60% were refugees and 40% economic migrants.
Tensions have been growing in Croatia as long lines of refugees wait to board trains and buses.
There were reports of clashes between desperate refugees from Afghanistan and Syria at the train station in Beli Manastir.
Elsewhere, some 2,000 people have gathered in Tovarnik waiting for transport.
Temperatures were in the high 30s and 100 people had sought treatment for heat exhaustion and severe dehydration.
EU leaders are to meet next Wednesday to try to agree a unified response to what has become the biggest movement of people in Europe since World War Two.
Meanwhile, the Vatican said it had taken in a family of four from Syria, following a call by Pope Francis for every Church parish to house refugees.
