Hungary erected a steel gate and fence posts at a border crossing with Croatia on Sunday, moving to seal a route used by its southern neighbor to offload thousands of migrants, a Reuters cameraman said.
Croatia has sent dozens of buses packed with migrants through the Baranjsko Petrovo Selo Beremend crossing since they began streaming over its eastern border with Serbia five days ago.
More still have crossed by train, boarded by hundreds in chaotic scenes repeated on Sunday when rain-soaked migrants climbed through carriage windows at the Croatian border station of Tovarnik.
Hungary has barred their entry into the European Union via its border with Serbia with a metal fence and a raft of strict asylum rules, forcing them west into Croatia.
Fast losing control over an influx of some 25,000 migrants, Croatia the EU's newest member has taken to sending them north by bus and train across its own border with Hungary, which has waved them on to Austria.
The move has triggered angry exchanges between Zagreb and Budapest indicative of the disarray in Europe over the largest migration of people westwards since World War Two.
Hungary, which says it is defending Europe's "Christian identity" from hundreds of thousands of mainly Muslim migrants reaching its shores, says it is completing another fence on a 41 kilometer (25.5 miles) stretch of its frontier with Croatia to keep them out.
A Reuters cameraman on the Croatian side of the border saw construction crews and soldiers erecting a gate and driving fence posts some three meters high into the ground, suggesting they were close to sealing the Beremend crossing.
More migrant buses were on their way from the nearby Croatian town of Beli Manastir.
Further south, on Croatia's border with Serbia, a packed train left the town of Tovarnik amid desperate scenes of migrants running and fighting to board, and small children plucked from the crowd by startled and overwhelmed police.
After several hot days, the temperature dropped overnight and rain arrived on Sunday. "I'm desperate," said 32-year-old Amina, traveling with two children from Baquba in Iraq.
"It was cold overnight and now it's raining and the children will get sick," she said through a Red Cross interpreter. "The police say they will board women and children first, but I didn't manage. I lost our bag the day before yesterday and now we have no belongings at all."
(Writing by Matt Robinson; Editing by Tom Heneghan)